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| Meta Title | Other functions | ClickHouse Docs |
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| Boilerpipe Text | Note
The function documentation below is generated from the
system.functions
system table.
FQDN
β
Introduced in: v20.1.0
Returns the fully qualified domain name of the ClickHouse server.
Syntax
FQDN
(
)
Aliases
:
fullHostName
Arguments
None.
Returned value
Returns the fully qualified domain name of the ClickHouse server.
String
Examples
Usage example
Query
SELECT
fqdn
(
)
Response
ββFQDN()βββββββββββββββββββββββββββ
β clickhouse.us-east-2.internal β
βββββββββββββββββββββββββββββββββββ
MACNumToString
β
Introduced in: v1.1.0
Interprets a
UInt64
number as a MAC address in big endian format.
Returns the corresponding MAC address in format
AA:BB:CC:DD:EE:FF
(colon-separated numbers in hexadecimal form) as string.
Syntax
MACNumToString
(
num
)
Arguments
num
β UInt64 number.
UInt64
Returned value
Returns a MAC address in format AA:BB:CC:DD:EE:FF.
String
Examples
Usage example
Query
SELECT
MACNumToString
(
149809441867716
)
AS
mac_address
;
Response
ββmac_addressββββββββ
β 88:00:11:22:33:44 β
βββββββββββββββββββββ
MACStringToNum
β
Introduced in: v1.1.0
The inverse function of MACNumToString. If the MAC address has an invalid format, it returns 0.
Syntax
MACStringToNum
(
s
)
Arguments
s
β MAC address string.
String
Returned value
Returns a UInt64 number.
UInt64
Examples
Usage example
Query
SELECT
MACStringToNum
(
'01:02:03:04:05:06'
)
AS
mac_numeric
;
Response
1108152157446
MACStringToOUI
β
Introduced in: v1.1.0
Given a MAC address in format AA:BB:CC:DD:EE:FF (colon-separated numbers in hexadecimal form), returns the first three octets as a UInt64 number. If the MAC address has an invalid format, it returns 0.
Syntax
MACStringToOUI
(
s
)
Arguments
s
β MAC address string.
String
Returned value
First three octets as UInt64 number.
UInt64
Examples
Usage example
Query
SELECT
MACStringToOUI
(
'00:50:56:12:34:56'
)
AS
oui
;
Response
20566
authenticatedUser
β
Introduced in: v25.11.0
If the session user has been switched using the EXECUTE AS command, this function returns the name of the original user that was used for authentication and creating the session.
Alias: authUser()
Syntax
authenticatedUser
(
)
Aliases
:
authUser
Arguments
None.
Returned value
The name of the authenticated user.
String
Examples
Usage example
Query
EXECUTE
as
u1
;
SELECT
currentUser
(
)
,
authenticatedUser
(
)
;
Response
ββcurrentUser()ββ¬βauthenticatedUser()ββ
β u1 β default β
βββββββββββββββββ΄ββββββββββββββββββββββ
bar
β
Introduced in: v1.1.0
Builds a bar chart.
Draws a band with width proportional to (x - min) and equal to width characters when x = max.
The band is drawn with accuracy to one eighth of a symbol.
Syntax
bar
(
x
,
min
,
max
[
,
width
]
)
Arguments
x
β Size to display.
(U)Int*
or
Float*
or
Decimal
min
β The minimum value.
(U)Int*
or
Float*
or
Decimal
max
β The maximum value.
(U)Int*
or
Float*
or
Decimal
width
β Optional. The width of the bar in characters. The default is
80
.
const (U)Int*
or
const Float*
or
const Decimal
Returned value
Returns a unicode-art bar string.
String
Examples
Usage example
Query
SELECT
toHour
(
EventTime
)
AS
h
,
count
(
)
AS
c
,
bar
(
c
,
0
,
600000
,
20
)
AS
bar
FROM
test
.
hits
GROUP
BY
h
ORDER
BY
h
ASC
Response
βββhββ¬ββββββcββ¬βbarβββββββββββββββββ
β 0 β 292907 β ββββββββββ β
β 1 β 180563 β ββββββ β
β 2 β 114861 β ββββ β
β 3 β 85069 β βββ β
β 4 β 68543 β βββ β
β 5 β 78116 β βββ β
β 6 β 113474 β ββββ β
β 7 β 170678 β ββββββ β
β 8 β 278380 β ββββββββββ β
β 9 β 391053 β βββββββββββββ β
β 10 β 457681 β ββββββββββββββββ β
β 11 β 493667 β βββββββββββββββββ β
β 12 β 509641 β βββββββββββββββββ β
β 13 β 522947 β ββββββββββββββββββ β
β 14 β 539954 β ββββββββββββββββββ β
β 15 β 528460 β ββββββββββββββββββ β
β 16 β 539201 β ββββββββββββββββββ β
β 17 β 523539 β ββββββββββββββββββ β
β 18 β 506467 β βββββββββββββββββ β
β 19 β 520915 β ββββββββββββββββββ β
β 20 β 521665 β ββββββββββββββββββ β
β 21 β 542078 β ββββββββββββββββββ β
β 22 β 493642 β βββββββββββββββββ β
β 23 β 400397 β ββββββββββββββ β
ββββββ΄βββββββββ΄βββββββββββββββββββββ
blockNumber
β
Introduced in: v1.1.0
Returns a monotonically increasing sequence number of the
block
containing the row.
The returned block number is updated on a best-effort basis, i.e. it may not be fully accurate.
Syntax
blockNumber
(
)
Arguments
None.
Returned value
Sequence number of the data block where the row is located.
UInt64
Examples
Basic usage
Query
SELECT
blockNumber
(
)
FROM
(
SELECT
*
FROM
system
.
numbers
LIMIT
10
)
SETTINGS max_block_size
=
2
Response
ββblockNumber()ββ
β 7 β
β 7 β
βββββββββββββββββ
ββblockNumber()ββ
β 8 β
β 8 β
βββββββββββββββββ
ββblockNumber()ββ
β 9 β
β 9 β
βββββββββββββββββ
ββblockNumber()ββ
β 10 β
β 10 β
βββββββββββββββββ
ββblockNumber()ββ
β 11 β
β 11 β
βββββββββββββββββ
blockSerializedSize
β
Introduced in: v20.3.0
Returns the uncompressed size in bytes of a block of values on disk.
Syntax
blockSerializedSize
(
x1
[
,
x2
[
,
.
.
.
]
]
)
Arguments
x1[, x2, ...]
β Any number of values for which to get the uncompressed size of the block.
Any
Returned value
Returns the number of bytes that will be written to disk for a block of values without compression.
UInt64
Examples
Usage example
Query
SELECT
blockSerializedSize
(
maxState
(
1
)
)
AS
x
;
Response
ββxββ
β 2 β
βββββ
blockSize
β
Introduced in: v1.1.0
In ClickHouse, queries are processed in
blocks
(chunks).
This function returns the size (row count) of the block the function is called on.
Syntax
blockSize
(
)
Arguments
None.
Returned value
Returns the number of rows in the current block.
UInt64
Examples
Usage example
Query
SELECT
blockSize
(
)
FROM
system
.
numbers
LIMIT
5
Response
ββblockSize()ββ
β 5 β
β 5 β
β 5 β
β 5 β
β 5 β
βββββββββββββββ
buildId
β
Introduced in: v20.5.0
Returns the build ID generated by a compiler for the running ClickHouse server binary.
If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard.
Otherwise it produces a constant value.
Syntax
buildId
(
)
Arguments
None.
Returned value
Returns the build ID.
String
Examples
Usage example
Query
SELECT
buildId
(
)
Response
ββbuildId()βββββββββββββββββββββββββββββββββ
β AB668BEF095FAA6BD26537F197AC2AF48A927FB4 β
ββββββββββββββββββββββββββββββββββββββββββββ
byteSize
β
Introduced in: v21.1.0
Returns an estimation of the uncompressed byte size of its arguments in memory.
For
String
arguments, the function returns the string length + 8 (length).
If the function has multiple arguments, the function accumulates their byte sizes.
Syntax
byteSize
(
arg1
[
,
arg2
,
.
.
.
]
)
Arguments
arg1[, arg2, ...]
β Values of any data type for which to estimate the uncompressed byte size.
Any
Returned value
Returns an estimation of the byte size of the arguments in memory.
UInt64
Examples
Usage example
Query
SELECT
byteSize
(
'string'
)
Response
ββbyteSize('string')ββ
β 15 β
ββββββββββββββββββββββ
Multiple arguments
Query
SELECT
byteSize
(
NULL
,
1
,
0.3
,
''
)
Response
ββbyteSize(NULL, 1, 0.3, '')ββ
β 19 β
ββββββββββββββββββββββββββββββ
catboostEvaluate
β
Introduced in: v22.9.0
Evaluate an external catboost model.
CatBoost
is an open-source gradient boosting library developed by Yandex for machine learning.
Accepts a path to a catboost model and model arguments (features).
Prerequisites
Build the catboost evaluation library
Before evaluating catboost models, the
libcatboostmodel.<so|dylib>
library must be made available. See
CatBoost documentation
how to compile it.
Next, specify the path to
libcatboostmodel.<so|dylib>
in the clickhouse configuration:
<
clickhouse
>
...
<
catboost_lib_path
>
/path/to/libcatboostmodel.so
</
catboost_lib_path
>
...
</
clickhouse
>
For security and isolation reasons, the model evaluation does not run in the server process but in the clickhouse-library-bridge process.
At the first execution of
catboostEvaluate()
, the server starts the library bridge process if it is not running already. Both processes
communicate using a HTTP interface. By default, port
9012
is used. A different port can be specified as follows - this is useful if port
9012
is already assigned to a different service.
<
library_bridge
>
<
port
>
9019
</
port
>
</
library_bridge
>
Train a catboost model using libcatboost
See
Training and applying models
for how to train catboost models from a training data set.
Syntax
catboostEvaluate
(
path_to_model
,
feature_1
[
,
feature_2
,
.
.
.
,
feature_n
]
)
Arguments
path_to_model
β Path to catboost model.
const String
feature
β One or more model features/arguments.
Float*
Returned value
Returns the model evaluation result.
Float64
Examples
catboostEvaluate
Query
SELECT
catboostEvaluate
(
'/root/occupy.bin'
,
Temperature
,
Humidity
,
Light
,
CO2
,
HumidityRatio
)
AS
prediction
FROM
occupancy
LIMIT
1
Response
4.695691092573497
colorOKLABToSRGB
β
Introduced in: v26.2.0
Converts a color from the OKLab perceptual color space to the sRGB color space.
The input color is specified in the OKLab color space. If the input values are outside
the typical OKLab ranges, the result is implementation-defined.
OKLab uses three components:
L: perceptual lightness (typically in the range [0..1])
a: green-red opponent axis
b: blue-yellow opponent axis
The a and b components are theoretically unbounded, but in practice are between -0.4 and 0.4.
OKLab is designed to be perceptually uniform
while remaining inexpensive to compute.
The conversion is intended to be the inverse of colorSRGBToOKLAB and consists of
the following stages:
Conversion from OKLab to linear sRGB.
Conversion from linear sRGB to gamma-encoded sRGB.
The optional gamma argument specifies the exponent used when converting from linear
sRGB to gamma-encoded RGB values. If not specified, a default gamma value is used
for consistency with colorSRGBToOKLAB.
For more information about the OKLab color space and its relationship to sRGB, see
https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/color_value/oklab
.
Syntax
colorOKLABToSRGB
(
tuple
[
,
gamma
]
)
Arguments
tuple
β A tuple of three numeric values
L
,
a
,
b
, where
L
is in the range
[0...1]
.
Tuple(Float64, Float64, Float64)
gamma
β Optional. The exponent that is used to transform linear sRGB back to sRGB by applying
(x ^ (1 / gamma)) * 255
for each channel
x
. Defaults to
2.2
.
Float64
Returned value
Returns a tuple (R, G, B) representing sRGB color values.
Tuple(Float64, Float64, Float64)
Examples
Convert OKLAB to sRGB (Float)
Query
SELECT
colorOKLABToSRGB
(
(
0.4466
,
0.0991
,
0.44
)
)
AS
rgb
;
Response
ββrgbβββββββββββββββββββββββ
β (198.07056923258935,0,0) β
ββββββββββββββββββββββββββββ
Convert OKLAB to sRGB (UInt8)
Query
WITH
colorOKLABToSRGB
(
(
0.7
,
0.1
,
0.54
)
)
AS
t
SELECT
tuple
(
toUInt8
(
t
.
1
)
,
toUInt8
(
t
.
2
)
,
toUInt8
(
t
.
3
)
)
AS
RGB
;
Response
ββRGBβββββββββββ
β (255,0,0) β
ββββββββββββββββ
colorOKLCHToSRGB
β
Introduced in: v25.7.0
Converts a colour from the
OKLCH
perceptual colour space to the familiar
sRGB
colour space.
If
L
is outside the range
[0...1]
,
C
is negative, or
H
is outside the range
[0...360]
, the result is implementation-defined.
Note
OKLCH
is a cylindrical version of the OKLab colour space.
It's three coordinates are
L
(the lightness in the range
[0...1]
),
C
(chroma
>= 0
) and
H
(hue in degrees from
[0...360]
).
OKLab/OKLCH is designed to be perceptually uniform while remaining cheap to compute.
The conversion is the inverse of
colorSRGBToOKLCH
:
OKLCH to OKLab.
OKLab to Linear sRGB
Linear sRGB to sRGB
The second argument gamma is used at the last stage.
For references of colors in OKLCH space, and how they correspond to sRGB colors please see
https://oklch.com/
.
Syntax
colorOKLCHToSRGB(tuple [, gamma])
Arguments
tuple
β A tuple of three numeric values
L
,
C
,
H
, where
L
is in the range
[0...1]
,
C >= 0
and
H
is in the range
[0...360]
.
Tuple(Float64, Float64, Float64)
gamma
β Optional. The exponent that is used to transform linear sRGB back to sRGB by applying
(x ^ (1 / gamma)) * 255
for each channel
x
. Defaults to
2.2
.
Float64
Returned value
Returns a tuple (R, G, B) representing sRGB color values.
Tuple(Float64, Float64, Float64)
Examples
Convert OKLCH to sRGB
SELECT colorOKLCHToSRGB((0.6, 0.12, 40)) AS rgb;
ββrgbββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (186.02058688365264,100.68677189684993,71.67819977081575) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
Convert OKLCH to sRGB (UInt8)
WITH colorOKLCHToSRGB((0.6, 0.12, 40)) AS t
SELECT tuple(toUInt8(t.1), toUInt8(t.2), toUInt8(t.3)) AS RGB;
ββRGBβββββββββββ
β (186,100,71) β
ββββββββββββββββ
colorSRGBToOKLAB
β
Introduced in: v26.2.0
Converts a colour encoded in the
sRGB
colour space to the perceptually uniform
OKLAB
colour space.
If any input channel is outside
[0...255]
or the gamma value is non-positive, the behaviour is implementation-defined.
Note
OKLAB
is a perceptually uniform color space.
Its three coordinates are
L
(the lightness in the range
[0...1]
),
a (Green-Red axis)
and
b (Blue-Yellow axis)
.
OKLab is designed to be perceptually uniform while remaining cheap to compute.
The conversion consists of two stages:
sRGB to Linear sRGB
Linear sRGB to OKLab
Syntax
colorSRGBToOKLAB(tuple[, gamma])
Arguments
tuple
β Tuple of three values R, G, B in the range
[0...255]
.
Tuple(UInt8, UInt8, UInt8)
gamma
β Optional. Exponent that is used to linearize sRGB by applying
(x / 255)^gamma
to each channel
x
. Defaults to
2.2
.
Float64
Returned value
Returns a tuple (L, a, b) representing the OKLAB color space values.
Tuple(Float64, Float64, Float64)
Examples
Convert sRGB to OKLAB
SELECT colorSRGBToOKLAB((128, 64, 32), 2.2) AS lab;
ββlabβββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (0.4436238384931984,0.07266246769242975,0.07500108778529994) β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
colorSRGBToOKLCH
β
Introduced in: v25.7.0
Converts a colour encoded in the
sRGB
colour space to the perceptually uniform
OKLCH
colour space.
If any input channel is outside
[0...255]
or the gamma value is non-positive, the behaviour is implementation-defined.
Note
OKLCH
is a cylindrical version of the OKLab colour space.
It's three coordinates are
L
(the lightness in the range
[0...1]
),
C
(chroma
>= 0
) and
H
(the hue in degrees from
[0...360]
).
OKLab/OKLCH is designed to be perceptually uniform while remaining cheap to compute.
The conversion consists of three stages:
sRGB to Linear sRGB
Linear sRGB to OKLab
OKLab to OKLCH.
For references of colors in the OKLCH space, and how they correspond to sRGB colors, please see
https://OKLCH.com/
.
Syntax
colorSRGBToOKLCH(tuple[, gamma])
Arguments
tuple
β Tuple of three values R, G, B in the range
[0...255]
.
Tuple(UInt8, UInt8, UInt8)
gamma
β Optional. Exponent that is used to linearize sRGB by applying
(x / 255)^gamma
to each channel
x
. Defaults to
2.2
.
Float64
Returned value
Returns a tuple (L, C, H) representing the OKLCH color space values.
Tuple(Float64, Float64, Float64)
Examples
Convert sRGB to OKLCH
SELECT colorSRGBToOKLCH((128, 64, 32), 2.2) AS lch;
ββlchββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (0.4436238384931984,0.1044269954567863,45.90734548193018) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
connectionId
β
Introduced in: v21.3.0
Returns the connection ID of the client that submitted the current query.
This function is most useful in debugging scenarios.
It was created for compatibility with MySQL's
CONNECTION_ID
function.
It is not typically used in production queries.
Syntax
connectionId()
Arguments
None.
Returned value
Returns the connection ID of the current client.
UInt64
Examples
Usage example
SELECT connectionId();
ββconnectionId()ββ
β 0 β
ββββββββββββββββββ
countDigits
β
Introduced in: v20.8.0
Returns the number of decimal digits needed to represent a value.
Note
This function takes into account the scales of decimal values i.e., it calculates the result over the underlying integer type which is
(value * scale)
.
For example:
countDigits(42) = 2
countDigits(42.000) = 5
countDigits(0.04200) = 4
Tip
You can check decimal overflow for
Decimal64
with
countDigits(x) > 18
,
although it is slower than
isDecimalOverflow
.
Syntax
countDigits(x)
Arguments
x
β An integer or decimal value.
(U)Int*
or
Decimal
Returned value
Returns the number of digits needed to represent
x
.
UInt8
Examples
Usage example
SELECT countDigits(toDecimal32(1, 9)), countDigits(toDecimal32(-1, 9)),
countDigits(toDecimal64(1, 18)), countDigits(toDecimal64(-1, 18)),
countDigits(toDecimal128(1, 38)), countDigits(toDecimal128(-1, 38));
ββcountDigits(toDecimal32(1, 9))ββ¬βcountDigits(toDecimal32(-1, 9))ββ¬βcountDigits(toDecimal64(1, 18))ββ¬βcountDigits(toDecimal64(-1, 18))ββ¬βcountDigits(toDecimal128(1, 38))ββ¬βcountDigits(toDecimal128(-1, 38))ββ
β 10 β 10 β 19 β 19 β 39 β 39 β
ββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββ
currentDatabase
β
Introduced in: v1.1.0
Returns the name of the current database.
Useful in table engine parameters of
CREATE TABLE
queries where you need to specify the database.
Also see the
SET
statement
.
Syntax
currentDatabase()
Aliases
:
current_database
,
SCHEMA
,
DATABASE
Arguments
None.
Returned value
Returns the current database name.
String
Examples
Usage example
SELECT currentDatabase()
ββcurrentDatabase()ββ
β default β
βββββββββββββββββββββ
SQL standard syntax without parentheses
SELECT CURRENT_DATABASE
ββCURRENT_DATABASEββ
β default β
ββββββββββββββββββββ
currentProfiles
β
Introduced in: v21.9.0
Returns an array of the setting profiles for the current user.
Syntax
currentProfiles()
Arguments
None.
Returned value
Returns an array of setting profiles for the current user.
Array(String)
Examples
Usage example
SELECT currentProfiles();
ββcurrentProfiles()ββββββββββββββββββββββββββββββ
β ['default', 'readonly_user', 'web_analytics'] β
βββββββββββββββββββββββββββββββββββββββββββββββββ
currentQueryID
β
Introduced in: v25.2.0
Returns current Query id.
Syntax
currentQueryID()
Aliases
:
current_query_id
Arguments
None.
Returned value
Examples
Example
SELECT currentQueryID();
ββcurrentQueryID()ββββββββββββββββββββββ
β 1280d0e8-1a08-4524-be6e-77975bb68e7d β
ββββββββββββββββββββββββββββββββββββββββ
currentRoles
β
Introduced in: v21.9.0
Returns an array of the roles which are assigned to the current user.
Syntax
currentRoles()
Arguments
None.
Returned value
Returns an array of the roles which are assigned to the current user.
Array(String)
Examples
Usage example
SELECT currentRoles();
ββcurrentRoles()ββββββββββββββββββββββββββββββββββ
β ['sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
currentSchemas
β
Introduced in: v23.7.0
Same as function
currentDatabase
but
accepts a boolean argument which is ignored
returns the database name as an array with a single value.
Function
currentSchemas
only exists for compatibility with PostgreSQL.
Please use
currentDatabase
instead.
Also see the
SET
statement
.
Syntax
currentSchemas(bool)
Aliases
:
current_schemas
Arguments
bool
β A boolean value, which is ignored.
Bool
Returned value
Returns a single-element array with the name of the current database.
Array(String)
Examples
Usage example
SELECT currentSchemas(true)
ββcurrentSchemas(true)ββ
β ['default'] β
ββββββββββββββββββββββββ
currentUser
β
Introduced in: v20.1.0
Returns the name of the current user.
In case of a distributed query, the name of the user who initiated the query is returned.
Syntax
currentUser()
Aliases
:
current_user
,
user
Arguments
None.
Returned value
Returns the name of the current user, otherwise the login of the user who initiated the query.
String
Examples
Usage example
SELECT currentUser()
ββcurrentUser()ββ
β default β
βββββββββββββββββ
SQL standard syntax without parentheses
SELECT CURRENT_USER
ββCURRENT_USERββ
β default β
ββββββββββββββββ
defaultProfiles
β
Introduced in: v21.9.0
Returns an array of default setting profile names for the current user.
Syntax
defaultProfiles()
Arguments
None.
Returned value
Returns an array of default setting profile names for the current user.
Array(String)
Examples
Usage example
SELECT defaultProfiles();
ββdefaultProfiles()ββ
β ['default'] β
βββββββββββββββββββββ
defaultRoles
β
Introduced in: v21.9.0
Returns an array of default roles for the current user.
Syntax
defaultRoles()
Arguments
None.
Returned value
Returns an array of default roles for the current user.
Array(String)
Examples
Usage example
SELECT defaultRoles();
ββdefaultRoles()ββββββββββββββββββββββββββββββββββ
β ['sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
defaultValueOfArgumentType
β
Introduced in: v1.1.0
Returns the default value for a given data type.
Does not include default values for custom columns set by the user.
Syntax
defaultValueOfArgumentType(expression)
Arguments
expression
β Arbitrary type of value or an expression that results in a value of an arbitrary type.
Any
Returned value
Returns
0
for numbers, an empty string for strings or
NULL
for Nullable types.
UInt8
or
String
or
NULL
Examples
Usage example
SELECT defaultValueOfArgumentType(CAST(1 AS Int8));
ββdefaultValueOfArgumentType(CAST(1, 'Int8'))ββ
β 0 β
βββββββββββββββββββββββββββββββββββββββββββββββ
Nullable example
SELECT defaultValueOfArgumentType(CAST(1 AS Nullable(Int8)));
ββdefaultValueOfArgumentType(CAST(1, 'Nullable(Int8)'))ββ
β α΄Ία΅α΄Έα΄Έ β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
defaultValueOfTypeName
β
Introduced in: v1.1.0
Returns the default value for the given type name.
Syntax
defaultValueOfTypeName(type)
Arguments
type
β A string representing a type name.
String
Returned value
Returns the default value for the given type name:
0
for numbers, an empty string for strings, or
NULL
for Nullable
UInt8
or
String
or
NULL
Examples
Usage example
SELECT defaultValueOfTypeName('Int8');
ββdefaultValueOfTypeName('Int8')ββ
β 0 β
ββββββββββββββββββββββββββββββββββ
Nullable example
SELECT defaultValueOfTypeName('Nullable(Int8)');
ββdefaultValueOfTypeName('Nullable(Int8)')ββ
β α΄Ία΅α΄Έα΄Έ β
ββββββββββββββββββββββββββββββββββββββββββββ
displayName
β
Introduced in: v22.11.0
Returns the value of
display_name
from
config
or the server's Fully Qualified Domain Name (FQDN) if not set.
Syntax
displayName()
Arguments
None.
Returned value
Returns the value of
display_name
from config or server FQDN if not set.
String
Examples
Usage example
SELECT displayName();
ββdisplayName()ββ
β production β
βββββββββββββββββ
dumpColumnStructure
β
Introduced in: v1.1.0
Outputs a detailed description of the internal structure of a column and its data type.
Syntax
dumpColumnStructure(x)
Arguments
x
β Value for which to get the description of.
Any
Returned value
Returns a description of the column structure used for representing the value.
String
Examples
Usage example
SELECT dumpColumnStructure(CAST('2018-01-01 01:02:03', 'DateTime'));
ββdumpColumnStructure(CAST('2018-01-01 01:02:03', 'DateTime'))ββ
β DateTime, Const(size = 1, UInt32(size = 1)) β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
enabledProfiles
β
Introduced in: v21.9.0
Returns an array of setting profile names which are enabled for the current user.
Syntax
enabledProfiles()
Arguments
None.
Returned value
Returns an array of setting profile names which are enabled for the current user.
Array(String)
Examples
Usage example
SELECT enabledProfiles();
ββenabledProfiles()ββββββββββββββββββββββββββββββββββββββββββββββββββ
β ['default', 'readonly_user', 'web_analytics', 'batch_processing'] β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
enabledRoles
β
Introduced in: v21.9.0
Returns an array of the roles which are enabled for the current user.
Syntax
enabledRoles()
Arguments
None.
Returned value
Returns an array of role names which are enabled for the current user.
Array(String)
Examples
Usage example
SELECT enabledRoles();
ββenabledRoles()ββββββββββββββββββββββββββββββββββββββββββββββββββ
β ['general_data', 'sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
errorCodeToName
β
Introduced in: v20.12.0
Returns the textual name of a numeric ClickHouse error code.
The mapping from numeric error codes to error names is available
here
.
Syntax
errorCodeToName(error_code)
Arguments
error_code
β ClickHouse error code.
(U)Int*
or
Float*
or
Decimal
Returned value
Returns the textual name of
error_code
.
String
Examples
Usage example
SELECT errorCodeToName(252);
ββerrorCodeToName(252)ββ
β TOO_MANY_PARTS β
ββββββββββββββββββββββββ
file
β
Introduced in: v21.3.0
Reads a file as a string and loads the data into the specified column.
The file content is not interpreted.
Also see the
file
table function.
Syntax
file(path[, default])
Arguments
path
β The path of the file relative to the
user_files_path
. Supports wildcards
*
,
**
,
?
,
{abc,def}
and
{N..M}
where
N
,
M
are numbers and
'abc', 'def'
are strings.
String
default
β The value returned if the file does not exist or cannot be accessed.
String
or
NULL
Returned value
Returns the file content as a string.
String
Examples
Insert files into a table
INSERT INTO table SELECT file('a.txt'), file('b.txt');
filesystemAvailable
β
Introduced in: v20.1.0
Returns the amount of free space in the filesystem hosting the database persistence.
The returned value is always smaller than the total free space (
filesystemUnreserved
) because some space is reserved for the operating system.
Syntax
filesystemAvailable([disk_name])
Arguments
disk_name
β Optional. The disk name to find the amount of free space for. If omitted, uses the default disk.
String
or
FixedString
Returned value
Returns the amount of remaining space available in bytes.
UInt64
Examples
Usage example
SELECT formatReadableSize(filesystemAvailable()) AS "Available space";
ββAvailable spaceββ
β 30.75 GiB β
βββββββββββββββββββ
filesystemCapacity
β
Introduced in: v20.1.0
Returns the capacity of the filesystem in bytes.
Needs the
path
to the data directory to be configured.
Syntax
filesystemCapacity([disk_name])
Arguments
disk_name
β Optional. The disk name to get the capacity for. If omitted, uses the default disk.
String
or
FixedString
Returned value
Returns the capacity of the filesystem in bytes.
UInt64
Examples
Usage example
SELECT formatReadableSize(filesystemCapacity()) AS "Capacity";
ββCapacityβββ
β 39.32 GiB β
βββββββββββββ
filesystemUnreserved
β
Introduced in: v22.12.0
Returns the total amount of free space on the filesystem hosting the database persistence (previously
filesystemFree
).
See also
filesystemAvailable
.
Syntax
filesystemUnreserved([disk_name])
Arguments
disk_name
β Optional. The disk name for which to find the total amount of free space. If omitted, uses the default disk.
String
or
FixedString
Returned value
Returns the amount of free space in bytes.
UInt64
Examples
Usage example
SELECT formatReadableSize(filesystemUnreserved()) AS "Free space";
ββFree spaceββ
β 32.39 GiB β
ββββββββββββββ
finalizeAggregation
β
Introduced in: v1.1.0
Given an aggregation state, this function returns the result of aggregation (or the finalized state when using a
-State
combinator).
Syntax
finalizeAggregation(state)
Arguments
state
β State of aggregation.
AggregateFunction
Returned value
Returns the finalized result of aggregation.
Any
Examples
Usage example
SELECT finalizeAggregation(arrayReduce('maxState', [1, 2, 3]));
ββfinalizeAggregation(arrayReduce('maxState', [1, 2, 3]))ββ
β 3 β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
Combined with initializeAggregation
WITH initializeAggregation('sumState', number) AS one_row_sum_state
SELECT
number,
finalizeAggregation(one_row_sum_state) AS one_row_sum,
runningAccumulate(one_row_sum_state) AS cumulative_sum
FROM numbers(5);
ββnumberββ¬βone_row_sumββ¬βcumulative_sumββ
β 0 β 0 β 0 β
β 1 β 1 β 1 β
β 2 β 2 β 3 β
β 3 β 3 β 6 β
β 4 β 4 β 10 β
ββββββββββ΄ββββββββββββββ΄βββββββββββββββββ
flipCoordinates
β
Introduced in: v25.10.0
Flips the x and y coordinates of geometric objects. This operation swaps latitude and longitude, which is useful for converting between different coordinate systems or correcting coordinate order.
For a Point, it swaps the x and y coordinates. For complex geometries (LineString, Polygon, MultiPolygon, Ring, MultiLineString), it recursively applies the transformation to each coordinate pair.
The function supports both individual geometry types (Point, Ring, Polygon, MultiPolygon, LineString, MultiLineString) and the Geometry variant type.
Syntax
flipCoordinates(geometry)
Arguments
geometry
β The geometry to transform. Supported types: Point (Tuple(Float64, Float64)), Ring (Array(Point)), Polygon (Array(Ring)), MultiPolygon (Array(Polygon)), LineString (Array(Point)), MultiLineString (Array(LineString)), or Geometry (a variant containing any of these types).
Returned value
The geometry with flipped coordinates. The return type matches the input type.
Point
or
Ring
or
Polygon
or
MultiPolygon
or
LineString
or
MultiLineString
or
Geometry
Examples
basic_point
SELECT flipCoordinates((1.0, 2.0));
(2.0, 1.0)
ring
SELECT flipCoordinates([(1.0, 2.0), (3.0, 4.0)]);
[(2.0, 1.0), (4.0, 3.0)]
polygon
SELECT flipCoordinates([[(1.0, 2.0), (3.0, 4.0)], [(5.0, 6.0), (7.0, 8.0)]]);
[[(2.0, 1.0), (4.0, 3.0)], [(6.0, 5.0), (8.0, 7.0)]]
geometry_wkt
SELECT flipCoordinates(readWkt('POINT(10 20)'));
(20, 10)
geometry_polygon_wkt
SELECT flipCoordinates(readWkt('POLYGON((0 0, 5 0, 5 5, 0 5, 0 0))'));
[[(0, 0), (0, 5), (5, 5), (5, 0), (0, 0)]]
formatQuery
β
Introduced in: v23.10.0
Returns a formatted, possibly multi-line, version of the given SQL query. Throws in case of a parsing error.
[example:multiline]
Syntax
formatQuery(query)
Arguments
query
β The SQL query to be formatted.
String
Returned value
The formatted query
String
Examples
multiline
SELECT formatQuery('select a, b FRom tab WHERE a > 3 and b < 3');
SELECT
a,
b
FROM tab
WHERE (a > 3) AND (b < 3)
formatQueryOrNull
β
Introduced in: v23.11.0
Returns a formatted, possibly multi-line, version of the given SQL query. Returns NULL in case of a parsing error.
[example:multiline]
Syntax
formatQueryOrNull(query)
Arguments
query
β The SQL query to be formatted.
String
Returned value
The formatted query
String
Examples
multiline
SELECT formatQuery('select a, b FRom tab WHERE a > 3 and b < 3');
SELECT
a,
b
FROM tab
WHERE (a > 3) AND (b < 3)
formatQuerySingleLine
β
Introduced in: v23.10.0
Like formatQuery() but the returned formatted string contains no line breaks. Throws in case of a parsing error.
[example:multiline]
Syntax
formatQuerySingleLine(query)
Arguments
query
β The SQL query to be formatted.
String
Returned value
The formatted query
String
Examples
multiline
SELECT formatQuerySingleLine('select a, b FRom tab WHERE a > 3 and b < 3');
SELECT a, b FROM tab WHERE (a > 3) AND (b < 3)
formatQuerySingleLineOrNull
β
Introduced in: v23.11.0
Like formatQuery() but the returned formatted string contains no line breaks. Returns NULL in case of a parsing error.
[example:multiline]
Syntax
formatQuerySingleLineOrNull(query)
Arguments
query
β The SQL query to be formatted.
String
Returned value
The formatted query
String
Examples
multiline
SELECT formatQuerySingleLine('select a, b FRom tab WHERE a > 3 and b < 3');
SELECT a, b FROM tab WHERE (a > 3) AND (b < 3)
formatReadableDecimalSize
β
Introduced in: v22.11.0
Given a size (number of bytes), this function returns a readable, rounded size with suffix (KB, MB, etc.) as a string.
The opposite operations of this function are
parseReadableSize
.
Syntax
formatReadableDecimalSize(x)
Arguments
x
β Size in bytes.
UInt64
Returned value
Returns a readable, rounded size with suffix as a string.
String
Examples
Format file sizes
SELECT
arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
formatReadableDecimalSize(filesize_bytes) AS filesize
ββfilesize_bytesββ¬βfilesizeββββ
β 1 β 1.00 B β
β 1024 β 1.02 KB β
β 1048576 β 1.05 MB β
β 192851925 β 192.85 MB β
ββββββββββββββββββ΄βββββββββββββ
formatReadableQuantity
β
Introduced in: v20.10.0
Given a number, this function returns a rounded number with suffix (thousand, million, billion, etc.) as a string.
This function accepts any numeric type as input, but internally it casts them to
Float64
.
Results might be suboptimal with large values.
Syntax
formatReadableQuantity(x)
Arguments
x
β A number to format.
UInt64
Returned value
Returns a rounded number with suffix as a string.
String
Examples
Format numbers with suffixes
SELECT
arrayJoin([1024, 1234 * 1000, (4567 * 1000) * 1000, 98765432101234]) AS number,
formatReadableQuantity(number) AS number_for_humans
ββββββββββnumberββ¬βnumber_for_humansββ
β 1024 β 1.02 thousand β
β 1234000 β 1.23 million β
β 4567000000 β 4.57 billion β
β 98765432101234 β 98.77 trillion β
ββββββββββββββββββ΄ββββββββββββββββββββ
formatReadableSize
β
Introduced in: v1.1.0
Given a size (number of bytes), this function returns a readable, rounded size with suffix (KiB, MiB, etc.) as string.
The opposite operations of this function are
parseReadableSize
,
parseReadableSizeOrZero
, and
parseReadableSizeOrNull
.
This function accepts any numeric type as input, but internally it casts them to
Float64
. Results might be suboptimal with large values.
Syntax
formatReadableSize(x)
Aliases
:
FORMAT_BYTES
Arguments
x
β Size in bytes.
UInt64
Returned value
Returns a readable, rounded size with suffix as a string.
String
Examples
Format file sizes
SELECT
arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
formatReadableSize(filesize_bytes) AS filesize
ββfilesize_bytesββ¬βfilesizeββββ
β 1 β 1.00 B β
β 1024 β 1.00 KiB β
β 1048576 β 1.00 MiB β
β 192851925 β 183.92 MiB β
ββββββββββββββββββ΄βββββββββββββ
formatReadableTimeDelta
β
Introduced in: v20.12.0
Given a time interval (delta) in seconds, this function returns a time delta with year/month/day/hour/minute/second/millisecond/microsecond/nanosecond as a string.
This function accepts any numeric type as input, but internally it casts them to
Float64
. Results might be suboptimal with large values.
Syntax
formatReadableTimeDelta(column[, maximum_unit, minimum_unit])
Arguments
column
β A column with a numeric time delta.
Float64
maximum_unit
β Optional. Maximum unit to show. Acceptable values:
nanoseconds
,
microseconds
,
milliseconds
,
seconds
,
minutes
,
hours
,
days
,
months
,
years
. Default value:
years
.
const String
minimum_unit
β Optional. Minimum unit to show. All smaller units are truncated. Acceptable values:
nanoseconds
,
microseconds
,
milliseconds
,
seconds
,
minutes
,
hours
,
days
,
months
,
years
. If explicitly specified value is bigger than
maximum_unit
, an exception will be thrown. Default value:
seconds
if
maximum_unit
is
seconds
or bigger,
nanoseconds
otherwise.
const String
Returned value
Returns a time delta as a string.
String
Examples
Usage example
SELECT
arrayJoin([100, 12345, 432546534]) AS elapsed,
formatReadableTimeDelta(elapsed) AS time_delta
βββββelapsedββ¬βtime_deltaββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β 100 β 1 minute and 40 seconds β
β 12345 β 3 hours, 25 minutes and 45 seconds β
β 432546534 β 13 years, 8 months, 17 days, 7 hours, 48 minutes and 54 secondsβ
ββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
With maximum unit
SELECT
arrayJoin([100, 12345, 432546534]) AS elapsed,
formatReadableTimeDelta(elapsed, 'minutes') AS time_delta
βββββelapsedββ¬βtime_deltaββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β 100 β 1 minute and 40 seconds β
β 12345 β 205 minutes and 45 seconds β
β 432546534 β 7209108 minutes and 54 seconds β
ββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
fuzzQuery
β
Introduced in: v26.2.0
Parses the given query string and applies random AST mutations (fuzzing) to it. Returns the fuzzed query as a string. Non-deterministic: each call may produce a different result. Requires
allow_fuzz_query_functions = 1
.
Syntax
fuzzQuery(query)
Arguments
query
β The SQL query to be fuzzed.
String
Returned value
The fuzzed query string
String
Examples
basic
SET allow_fuzz_query_functions = 1; SELECT fuzzQuery('SELECT 1');
generateRandomStructure
β
Introduced in: v23.5.0
Generates random table structure in the format
column1_name column1_type, column2_name column2_type, ...
.
Syntax
generateRandomStructure([number_of_columns, seed])
Arguments
number_of_columns
β The desired number of columns in the resultant table structure. If set to 0 or
Null
, the number of columns will be random from 1 to 128. Default value:
Null
.
UInt64
seed
β Random seed to produce stable results. If seed is not specified or set to
Null
, it is randomly generated.
UInt64
Returned value
Randomly generated table structure.
String
Examples
Usage example
SELECT generateRandomStructure()
c1 Decimal32(5), c2 Date, c3 Tuple(LowCardinality(String), Int128, UInt64, UInt16, UInt8, IPv6), c4 Array(UInt128), c5 UInt32, c6 IPv4, c7 Decimal256(64), c8 Decimal128(3), c9 UInt256, c10 UInt64, c11 DateTime
with specified number of columns
SELECT generateRandomStructure(1)
c1 Map(UInt256, UInt16)
with specified seed
SELECT generateRandomStructure(NULL, 33)
c1 DateTime, c2 Enum8('c2V0' = 0, 'c2V1' = 1, 'c2V2' = 2, 'c2V3' = 3), c3 LowCardinality(Nullable(FixedString(30))), c4 Int16, c5 Enum8('c5V0' = 0, 'c5V1' = 1, 'c5V2' = 2, 'c5V3' = 3), c6 Nullable(UInt8), c7 String, c8 Nested(e1 IPv4, e2 UInt8, e3 UInt16, e4 UInt16, e5 Int32, e6 Map(Date, Decimal256(70)))
generateSerialID
β
Introduced in: v25.1.0
Generates and returns sequential numbers starting from the previous counter value.
This function takes a string argument - a series identifier, and an optional starting value.
The server should be configured with Keeper.
The series are stored in Keeper nodes under the path, which can be configured in
series_keeper_path
in the server configuration.
Syntax
generateSerialID(series_identifier[, start_value])
Arguments
series_identifier
β Series identifier
const String
start_value
β Optional. Starting value for the counter. Defaults to 0. Note: this value is only used when creating a new series and is ignored if the series already exists
UInt*
Returned value
Returns sequential numbers starting from the previous counter value.
UInt64
Examples
first call
SELECT generateSerialID('id1')
ββgenerateSerialID('id1')βββ
β 1 β
ββββββββββββββββββββββββββββ
second call
SELECT generateSerialID('id1')
ββgenerateSerialID('id1')βββ
β 2 β
ββββββββββββββββββββββββββββ
column call
SELECT *, generateSerialID('id1') FROM test_table
ββCounterIDββ¬βUserIDββ¬βverββ¬βgenerateSerialID('id1')βββ
β 1 β 3 β 3 β 3 β
β 1 β 1 β 1 β 4 β
β 1 β 2 β 2 β 5 β
β 1 β 5 β 5 β 6 β
β 1 β 4 β 4 β 7 β
βββββββββββββ΄βββββββββ΄ββββββ΄βββββββββββββββββββββββββββ
with start value
SELECT generateSerialID('id2', 100)
ββgenerateSerialID('id2', 100)βββ
β 100 β
βββββββββββββββββββββββββββββββββ
with start value second call
SELECT generateSerialID('id2', 100)
ββgenerateSerialID('id2', 100)βββ
β 101 β
βββββββββββββββββββββββββββββββββ
Introduced in: v24.5.0
Gets the value of an HTTP header.
If there is no such header or the current request is not performed via the HTTP interface, the function returns an empty string.
Certain HTTP headers (e.g.,
Authentication
and
X-ClickHouse-*
) are restricted.
Note
Setting
allow_get_client_http_header
is required
The function requires the setting
allow_get_client_http_header
to be enabled.
The setting is not enabled by default for security reasons, because some headers, such as
Cookie
, could contain sensitive info.
HTTP headers are case sensitive for this function.
If the function is used in the context of a distributed query, it returns non-empty result only on the initiator node.
Syntax
getClientHTTPHeader(name)
Arguments
name
β The HTTP header name.
String
Returned value
Returns the value of the header.
String
Examples
Usage example
SELECT getClientHTTPHeader('Content-Type');
ββgetClientHTTPHeader('Content-Type')ββ
β application/x-www-form-urlencoded β
βββββββββββββββββββββββββββββββββββββββ
getMacro
β
Introduced in: v20.1.0
Returns the value of a macro from the server configuration file.
Macros are defined in the
<macros>
section of the configuration file and can be used to distinguish servers by convenient names even if they have complicated hostnames.
If the function is executed in the context of a distributed table, it generates a normal column with values relevant to each shard.
Syntax
getMacro(name)
Arguments
name
β The name of the macro to retrieve.
const String
Returned value
Returns the value of the specified macro.
String
Examples
Basic usage
SELECT getMacro('test');
ββgetMacro('test')ββ
β Value β
ββββββββββββββββββββ
getMaxTableNameLengthForDatabase
β
Introduced in: v25.1.0
Returns the maximum table name length in a specified database.
Syntax
getMaxTableNameLengthForDatabase(database_name)
Arguments
database_name
β The name of the specified database.
String
Returned value
Returns the length of the maximum table name, an Integer
Examples
typical
SELECT getMaxTableNameLengthForDatabase('default');
ββgetMaxTableNameLengthForDatabase('default')ββ
β 206 β
βββββββββββββββββββββββββββββββββββββββββββββββ
getMergeTreeSetting
β
Introduced in: v25.6.0
Returns the current value of a MergeTree setting.
Syntax
getMergeTreeSetting(setting_name)
Arguments
setting_name
β The setting name.
String
Returned value
Returns the merge tree setting's current value.
Examples
Usage example
SELECT getMergeTreeSetting('index_granularity');
ββgetMergeTreeSetting('index_granularity')ββ
β 8192 β
ββββββββββββββββββββββββββββββββββββββββββββ
getOSKernelVersion
β
Introduced in: v21.11.0
Returns a string with the OS kernel version.
Syntax
getOSKernelVersion()
Arguments
None.
Returned value
Returns the current OS kernel version.
String
Examples
Usage example
SELECT getOSKernelVersion();
ββgetOSKernelVersion()βββββ
β Linux 4.15.0-55-generic β
βββββββββββββββββββββββββββ
getServerPort
β
Introduced in: v21.10.0
Returns the server's port number for a given protocol.
Syntax
getServerPort(port_name)
Arguments
port_name
β The name of the port.
String
Returned value
Returns the server port number.
UInt16
Examples
Usage example
SELECT getServerPort('tcp_port');
ββgetServerPort('tcp_port')ββ
β 9000 β
βββββββββββββββββββββββββββββ
getServerSetting
β
Introduced in: v25.6.0
Returns the currently set value, given a server setting name.
Syntax
getServerSetting(setting_name')
Arguments
setting_name
β The server setting name.
String
Returned value
Returns the server setting's current value.
Any
Examples
Usage example
SELECT getServerSetting('allow_use_jemalloc_memory');
ββgetServerSetting('allow_use_jemalloc_memory')ββ
β true β
βββββββββββββββββββββββββββββββββββββββββββββββββ
getSetting
β
Introduced in: v20.7.0
Returns the current value of a setting.
Syntax
getSetting(setting_name)
Arguments
setting_Name
β The setting name.
const String
Returned value
Returns the setting's current value.
Any
Examples
Usage example
SELECT getSetting('enable_analyzer');
SET enable_analyzer = false;
SELECT getSetting('enable_analyzer');
ββgetSetting('β―_analyzer')ββ
β true β
ββββββββββββββββββββββββββββ
ββgetSetting('β―_analyzer')ββ
β false β
ββββββββββββββββββββββββββββ
getSettingOrDefault
β
Introduced in: v24.10.0
Returns the current value of a setting or returns the default value specified in the second argument if the setting is not set in the current profile.
Syntax
getSettingOrDefault(setting_name, default_value)
Arguments
setting_name
β The setting name.
String
default_value
β Value to return if custom_setting is not set. Value may be of any data type or Null.
Returned value
Returns the current value of the specified setting or
default_value
if the setting is not set.
Examples
Usage example
SELECT getSettingOrDefault('custom_undef1', 'my_value');
SELECT getSettingOrDefault('custom_undef2', 100);
SELECT getSettingOrDefault('custom_undef3', NULL);
my_value
100
NULL
getSizeOfEnumType
β
Introduced in: v1.1.0
Returns the number of fields in the given
Enum
.
Syntax
getSizeOfEnumType(x)
Arguments
x
β Value of type
Enum
.
Enum
Returned value
Returns the number of fields with
Enum
input values.
UInt8/16
Examples
Usage example
SELECT getSizeOfEnumType(CAST('a' AS Enum8('a' = 1, 'b' = 2))) AS x;
ββxββ
β 2 β
βββββ
getSubcolumn
β
Introduced in: v23.3.0
Receives the expression or identifier and constant string with the name of subcolumn.
Returns requested subcolumn extracted from the expression.
Syntax
getSubcolumn(nested_value, subcolumn_name)
Arguments
None.
Returned value
Examples
getSubcolumn
SELECT getSubcolumn(array_col, 'size0'), getSubcolumn(tuple_col, 'elem_name')
getTypeSerializationStreams
β
Introduced in: v22.6.0
Enumerates stream paths of a data type.
This function is intended for developmental use.
Syntax
getTypeSerializationStreams(col)
Arguments
col
β Column or string representation of a data-type from which the data type will be detected.
Any
Returned value
Returns an array with all the serialization sub-stream paths.
Array(String)
Examples
tuple
SELECT getTypeSerializationStreams(tuple('a', 1, 'b', 2))
['{TupleElement(1), Regular}','{TupleElement(2), Regular}','{TupleElement(3), Regular}','{TupleElement(4), Regular}']
map
SELECT getTypeSerializationStreams('Map(String, Int64)')
['{ArraySizes}','{ArrayElements, TupleElement(keys), Regular}','{ArrayElements, TupleElement(values), Regular}']
globalVariable
β
Introduced in: v20.5.0
Takes a constant string argument and returns the value of the global variable with that name. This function is intended for compatibility with MySQL and not needed or useful for normal operation of ClickHouse. Only few dummy global variables are defined.
Syntax
globalVariable(name)
Arguments
name
β Global variable name.
String
Returned value
Returns the value of variable
name
.
Any
Examples
globalVariable
SELECT globalVariable('max_allowed_packet')
67108864
hasColumnInTable
β
Introduced in: v1.1.0
Checks if a specific column exists in a database table.
For elements in a nested data structure, the function checks for the existence of a column.
For the nested data structure itself, the function returns
0
.
Syntax
hasColumnInTable([hostname[, username[, password]],]database, table, column)
Arguments
database
β Name of the database.
const String
table
β Name of the table.
const String
column
β Name of the column.
const String
hostname
β Optional. Remote server name to perform the check on.
const String
username
β Optional. Username for remote server.
const String
password
β Optional. Password for remote server.
const String
Returned value
Returns
1
if the given column exists,
0
otherwise.
UInt8
Examples
Check an existing column
SELECT hasColumnInTable('system','metrics','metric')
1
Check a non-existing column
SELECT hasColumnInTable('system','metrics','non-existing_column')
0
hasThreadFuzzer
β
Introduced in: v20.6.0
Returns whether the thread fuzzer is enabled.
THis function is only useful for testing and debugging.
Syntax
hasThreadFuzzer()
Arguments
None.
Returned value
Returns whether Thread Fuzzer is effective.
UInt8
Examples
Check Thread Fuzzer status
SELECT hasThreadFuzzer()
ββhasThreadFuzzer()ββ
β 0 β
βββββββββββββββββββββ
hostName
β
Introduced in: v20.5.0
Returns the name of the host on which this function was executed.
If the function executes on a remote server (distributed processing), the remote server name is returned.
If the function executes in the context of a distributed table, it generates a normal column with values relevant to each shard.
Otherwise it produces a constant value.
Syntax
hostName()
Aliases
:
hostname
Arguments
None.
Returned value
Returns the host name.
String
Examples
Usage example
SELECT hostName()
ββhostName()ββ
β clickhouse β
ββββββββββββββ
icebergBucket
β
Introduced in: v25.5.0
Implements logic for the
iceberg bucket transform
Syntax
icebergBucket(N, value)
Arguments
N
β The number of buckets, modulo.
const (U)Int*
value
β The source value to transform.
(U)Int*
or
Bool
or
Decimal
or
Float*
or
String
or
FixedString
or
UUID
or
Date
or
Time
or
DateTime
Returned value
Returns a 32-bit hash of the source value.
Int32
Examples
Example
SELECT icebergBucket(5, 1.0 :: Float32)
4
icebergTruncate
β
Introduced in: v25.3.0
Implements logic of iceberg truncate transform:
https://iceberg.apache.org/spec/#truncate-transform-details
.
Syntax
icebergTruncate(N, value)
Arguments
value
β The value to transform.
String
or
(U)Int*
or
Decimal
Returned value
The same type as the argument
Examples
Example
SELECT icebergTruncate(3, 'iceberg')
ice
identity
β
Introduced in: v1.1.0
This function returns the argument you pass to it, which is useful for debugging and testing. It lets you bypass index usage to see full scan performance instead. The query analyzer ignores anything inside identity functions when looking for indexes to use, and it also disables constant folding.
Syntax
identity(x)
Arguments
x
β Input value.
Any
Returned value
Returns the input value unchanged.
Any
Examples
Usage example
SELECT identity(42)
42
ignore
β
Introduced in: v1.1.0
Accepts arbitrary arguments and unconditionally returns
0
.
Syntax
ignore(x)
Arguments
x
β An input value which is unused and passed only so as to avoid a syntax error.
Any
Returned value
Always returns
0
.
UInt8
Examples
Usage example
SELECT ignore(0, 'ClickHouse', NULL)
ββignore(0, 'ClickHouse', NULL)ββ
β 0 β
βββββββββββββββββββββββββββββββββ
indexHint
β
Introduced in: v1.1.0
This function is intended for debugging and introspection.
It ignores its argument and always returns 1.
The arguments are not evaluated.
During index analysis, the argument of this function is assumed to not be wrapped in
indexHint
.
This allows you to select data in index ranges by the corresponding condition but without further filtering by this condition.
The index in ClickHouse is sparse and using
indexHint
will yield more data than specifying the same condition directly.
Explanation
Note: It is not possible to optimize a query with the
indexHint
function. The
indexHint
function does not optimize the query, as it does not provide any additional information for the query analysis. Having an expression inside the
indexHint
function is not anyhow better than without the
indexHint
function. The
indexHint
function can be used only for introspection and debugging purposes and it does not improve performance. If you see the usage of
indexHint
by anyone other than ClickHouse contributors, it is likely a mistake and you should remove it.
Syntax
indexHint(expression)
Arguments
expression
β Any expression for index range selection.
Expression
Returned value
Returns
1
in all cases.
UInt8
Examples
Usage example with date filtering
SELECT FlightDate AS k, count() FROM ontime WHERE indexHint(k = '2025-09-15') GROUP BY k ORDER BY k ASC;
βββββββββββkββ¬βcount()ββ
β 2025-09-14 β 7071 β
β 2025-09-15 β 16428 β
β 2025-09-16 β 1077 β
β 2025-09-30 β 8167 β
ββββββββββββββ΄ββββββββββ
initialQueryID
β
Introduced in: v1.1.0
Returns the ID of the initial current query.
Other parameters of a query can be extracted from field
initial_query_id
in
system.query_log
.
In contrast to
queryID
function,
initialQueryID
returns the same results on different shards.
Syntax
initialQueryID()
Aliases
:
initial_query_id
Arguments
None.
Returned value
Returns the ID of the initial current query.
String
Examples
Usage example
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT initialQueryID() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
ββcount(DISTINCT t)ββ
β 1 β
βββββββββββββββββββββ
initialQueryStartTime
β
Introduced in: v25.4.0
Returns the start time of the initial current query.
initialQueryStartTime
returns the same results on different shards.
Syntax
initialQueryStartTime()
Aliases
:
initial_query_start_time
Arguments
None.
Returned value
Returns the start time of the initial current query.
DateTime
Examples
Usage example
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT initialQueryStartTime() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
ββcount(DISTINCT t)ββ
β 1 β
βββββββββββββββββββββ
initializeAggregation
β
Introduced in: v20.6.0
Calculates the result of an aggregate function based on a single value.
This function can be used to initialize aggregate functions with combinator
-State
.
You can create states of aggregate functions and insert them to columns of type
AggregateFunction
or use initialized aggregates as default values.
Syntax
initializeAggregation(aggregate_function, arg1[, arg2, ...])
Arguments
aggregate_function
β Name of the aggregation function to initialize.
String
arg1[, arg2, ...]
β Arguments of the aggregate function.
Any
Returned value
Returns the result of aggregation for every row passed to the function. The return type is the same as the return type of the function that
initializeAggregation
takes as a first argument.
Any
Examples
Basic usage with uniqState
SELECT uniqMerge(state) FROM (SELECT initializeAggregation('uniqState', number % 3) AS state FROM numbers(10000));
ββuniqMerge(state)ββ
β 3 β
ββββββββββββββββββββ
Usage with sumState and finalizeAggregation
SELECT finalizeAggregation(state), toTypeName(state) FROM (SELECT initializeAggregation('sumState', number % 3) AS state FROM numbers(5));
ββfinalizeAggregation(state)ββ¬βtoTypeName(state)ββββββββββββββ
β 0 β AggregateFunction(sum, UInt8) β
β 1 β AggregateFunction(sum, UInt8) β
β 2 β AggregateFunction(sum, UInt8) β
β 0 β AggregateFunction(sum, UInt8) β
β 1 β AggregateFunction(sum, UInt8) β
ββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββ
isConstant
β
Introduced in: v20.3.0
Returns whether the argument is a constant expression.
A constant expression is an expression whose result is known during query analysis, i.e. before execution.
For example, expressions over
literals
are constant expressions.
This function is mostly intended for development, debugging and demonstration.
Syntax
isConstant(x)
Arguments
x
β An expression to check.
Any
Returned value
Returns
1
if
x
is constant,
0
if
x
is non-constant.
UInt8
Examples
Constant expression
SELECT isConstant(x + 1)
FROM (SELECT 43 AS x)
ββisConstant(plus(x, 1))ββ
β 1 β
ββββββββββββββββββββββββββ
Constant with function
WITH 3.14 AS pi
SELECT isConstant(cos(pi))
ββisConstant(cos(pi))ββ
β 1 β
βββββββββββββββββββββββ
Non-constant expression
SELECT isConstant(number)
FROM numbers(1)
ββisConstant(number)ββ
β 0 β
ββββββββββββββββββββββ
Behavior of the now() function
SELECT isConstant(now())
ββisConstant(now())ββ
β 1 β
βββββββββββββββββββββ
isDecimalOverflow
β
Introduced in: v20.8.0
Checks if a decimal number has too many digits to fit properly in a Decimal data type with given precision.
Syntax
isDecimalOverflow(value[, precision])
Arguments
value
β Decimal value to check.
Decimal
precision
β Optional. The precision of the Decimal type. If omitted, the initial precision of the first argument is used.
UInt8
Returned value
Returns
1
if the decimal value has more digits than allowed by its precision,
0
if the decimal value satisfies the specified precision.
UInt8
Examples
Usage example
SELECT isDecimalOverflow(toDecimal32(1000000000, 0), 9),
isDecimalOverflow(toDecimal32(1000000000, 0)),
isDecimalOverflow(toDecimal32(-1000000000, 0), 9),
isDecimalOverflow(toDecimal32(-1000000000, 0));
ββisDecimalOverflow(toDecimal32(1000000000, 0), 9)ββ¬βisDecimalOverflow(toDecimal32(1000000000, 0))ββ¬βisDecimalOverflow(toDecimal32(-1000000000, 0), 9)ββ¬βisDecimalOverflow(toDecimal32(-1000000000, 0))ββ
β 1 β 1 β 1 β 1 β
ββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββ
joinGet
β
Introduced in: v18.16.0
Allows you to extract data from a table the same way as from a dictionary.
Gets data from Join tables using the specified join key.
Note
Only supports tables created with the
ENGINE = Join(ANY, LEFT, <join_keys>)
statement
.
Syntax
joinGet(join_storage_table_name, value_column, join_keys)
Arguments
join_storage_table_name
β An identifier which indicates where to perform the search. The identifier is searched in the default database (see parameter
default_database
in the config file). To override the default database, use the
USE database_name
query or specify the database and the table through a dot, like
database_name.table_name
.
String
value_column
β The name of the column of the table that contains required data.
const String
join_keys
β A list of join keys.
Any
Returned value
Returns list of values corresponded to list of keys.
Any
Examples
Usage example
CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13);
SELECT joinGet(db_test.id_val, 'val', toUInt32(1));
ββjoinGet(db_test.id_val, 'val', toUInt32(1))ββ
β 11 β
βββββββββββββββββββββββββββββββββββββββββββββββ
Usage with table from current database
USE db_test;
SELECT joinGet(id_val, 'val', toUInt32(2));
ββjoinGet(id_val, 'val', toUInt32(2))ββ
β 12 β
βββββββββββββββββββββββββββββββββββββββ
Using arrays as join keys
CREATE TABLE some_table (id1 UInt32, id2 UInt32, name String) ENGINE = Join(ANY, LEFT, id1, id2);
INSERT INTO some_table VALUES (1, 11, 'a') (2, 12, 'b') (3, 13, 'c');
SELECT joinGet(some_table, 'name', 1, 11);
ββjoinGet(some_table, 'name', 1, 11)ββ
β a β
ββββββββββββββββββββββββββββββββββββββ
joinGetOrNull
β
Introduced in: v20.4.0
Allows you to extract data from a table the same way as from a dictionary.
Gets data from Join tables using the specified join key.
Unlike
joinGet
it returns
NULL
when the key is missing.
Note
Only supports tables created with the
ENGINE = Join(ANY, LEFT, <join_keys>)
statement
.
Syntax
joinGetOrNull(join_storage_table_name, value_column, join_keys)
Arguments
join_storage_table_name
β An identifier which indicates where to perform the search. The identifier is searched in the default database (see parameter default_database in the config file). To override the default database, use the
USE database_name
query or specify the database and the table through a dot, like
database_name.table_name
.
String
value_column
β The name of the column of the table that contains required data.
const String
join_keys
β A list of join keys.
Any
Returned value
Returns a list of values corresponding to the list of keys, or
NULL
if a key is not found.
Any
Examples
Usage example
CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13);
SELECT joinGetOrNull(db_test.id_val, 'val', toUInt32(1)), joinGetOrNull(db_test.id_val, 'val', toUInt32(999));
ββjoinGetOrNull(db_test.id_val, 'val', toUInt32(1))ββ¬βjoinGetOrNull(db_test.id_val, 'val', toUInt32(999))ββ
β 11 β α΄Ία΅α΄Έα΄Έ β
βββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββββ
lowCardinalityIndices
β
Introduced in: v18.12.0
Returns the position of a value in the dictionary of a
LowCardinality
column. Positions start at 1. Since LowCardinality have per-part dictionaries, this function may return different positions for the same value in different parts.
Syntax
lowCardinalityIndices(col)
Arguments
col
β A low cardinality column.
LowCardinality
Returned value
The position of the value in the dictionary of the current part.
UInt64
Examples
Usage examples
DROP TABLE IF EXISTS test;
CREATE TABLE test (s LowCardinality(String)) ENGINE = Memory;
-- create two parts:
INSERT INTO test VALUES ('ab'), ('cd'), ('ab'), ('ab'), ('df');
INSERT INTO test VALUES ('ef'), ('cd'), ('ab'), ('cd'), ('ef');
SELECT s, lowCardinalityIndices(s) FROM test;
ββsβββ¬βlowCardinalityIndices(s)ββ
β ab β 1 β
β cd β 2 β
β ab β 1 β
β ab β 1 β
β df β 3 β
ββββββ΄βββββββββββββββββββββββββββ
ββsβββ¬βlowCardinalityIndices(s)ββ
β ef β 1 β
β cd β 2 β
β ab β 3 β
β cd β 2 β
β ef β 1 β
ββββββ΄βββββββββββββββββββββββββββ
lowCardinalityKeys
β
Introduced in: v18.12.0
Returns the dictionary values of a
LowCardinality
column.
If the block is smaller or larger than the dictionary size, the result will be truncated or extended with default values.
Since LowCardinality have per-part dictionaries, this function may return different dictionary values in different parts.
Syntax
lowCardinalityKeys(col)
Arguments
col
β A low cardinality column.
LowCardinality
Returned value
Returns the dictionary keys.
UInt64
Examples
lowCardinalityKeys
DROP TABLE IF EXISTS test;
CREATE TABLE test (s LowCardinality(String)) ENGINE = Memory;
-- create two parts:
INSERT INTO test VALUES ('ab'), ('cd'), ('ab'), ('ab'), ('df');
INSERT INTO test VALUES ('ef'), ('cd'), ('ab'), ('cd'), ('ef');
SELECT s, lowCardinalityKeys(s) FROM test;
ββsβββ¬βlowCardinalityKeys(s)ββ
β ef β β
β cd β ef β
β ab β cd β
β cd β ab β
β ef β β
ββββββ΄ββββββββββββββββββββββββ
ββsβββ¬βlowCardinalityKeys(s)ββ
β ab β β
β cd β ab β
β ab β cd β
β ab β df β
β df β β
ββββββ΄ββββββββββββββββββββββββ
materialize
β
Introduced in: v1.1.0
Turns a constant into a full column containing a single value.
Full columns and constants are represented differently in memory.
Functions usually execute different code for normal and constant arguments, although the result should typically be the same.
This function can be used to debug this behavior.
Syntax
materialize(x)
Arguments
x
β A constant.
Any
Returned value
Returns a full column containing the constant value.
Any
Examples
Usage example
-- In the example below the `countMatches` function expects a constant second argument.
-- This behaviour can be debugged by using the `materialize` function to turn a constant into a full column,
-- verifying that the function throws an error for a non-constant argument.
SELECT countMatches('foobarfoo', 'foo');
SELECT countMatches('foobarfoo', materialize('foo'));
2
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Illegal type of argument #2 'pattern' of function countMatches, expected constant String, got String
minSampleSizeContinuous
β
Introduced in: v23.10.0
Calculates the minimum required sample size for an A/B test comparing means of a continuous metric in two samples.
Uses the formula described in
this article
.
Assumes equal sizes of treatment and control groups.
Returns the required sample size for one group (i.e. the sample size required for the whole experiment is twice the returned value).
Also assumes equal variance of the test metric in treatment and control groups.
Syntax
minSampleSizeContinuous(baseline, sigma, mde, power, alpha)
Aliases
:
minSampleSizeContinous
Arguments
baseline
β Baseline value of a metric.
(U)Int*
or
Float*
sigma
β Baseline standard deviation of a metric.
(U)Int*
or
Float*
mde
β Minimum detectable effect (MDE) as percentage of the baseline value (e.g. for a baseline value 112.25 the MDE 0.03 means an expected change to 112.25 Β± 112.25*0.03).
(U)Int*
or
Float*
power
β Required statistical power of a test (1 - probability of Type II error).
(U)Int*
or
Float*
alpha
β Required significance level of a test (probability of Type I error).
(U)Int*
or
Float*
Returned value
Returns a named Tuple with 3 elements:
minimum_sample_size
,
detect_range_lower
and
detect_range_upper
. These are respectively: the required sample size, the lower bound of the range of values not detectable with the returned required sample size, calculated as
baseline * (1 - mde)
, and the upper bound of the range of values not detectable with the returned required sample size, calculated as
baseline * (1 + mde)
(Float64).
Tuple(Float64, Float64, Float64)
Examples
minSampleSizeContinuous
SELECT minSampleSizeContinuous(112.25, 21.1, 0.03, 0.80, 0.05) AS sample_size
(616.2931945826209,108.8825,115.6175)
minSampleSizeConversion
β
Introduced in: v22.6.0
Calculates minimum required sample size for an A/B test comparing conversions (proportions) in two samples.
Uses the formula described in
this article
. Assumes equal sizes of treatment and control groups. Returns the sample size required for one group (i.e. the sample size required for the whole experiment is twice the returned value).
Syntax
minSampleSizeConversion(baseline, mde, power, alpha)
Arguments
baseline
β Baseline conversion.
Float*
mde
β Minimum detectable effect (MDE) as percentage points (e.g. for a baseline conversion 0.25 the MDE 0.03 means an expected change to 0.25 Β± 0.03).
Float*
power
β Required statistical power of a test (1 - probability of Type II error).
Float*
alpha
β Required significance level of a test (probability of Type I error).
Float*
Returned value
Returns a named Tuple with 3 elements:
minimum_sample_size
,
detect_range_lower
,
detect_range_upper
. These are, respectively: the required sample size, the lower bound of the range of values not detectable with the returned required sample size, calculated as
baseline - mde
, the upper bound of the range of values not detectable with the returned required sample size, calculated as
baseline + mde
.
Tuple(Float64, Float64, Float64)
Examples
minSampleSizeConversion
SELECT minSampleSizeConversion(0.25, 0.03, 0.80, 0.05) AS sample_size
(3396.077603219163,0.22,0.28)
neighbor
β
Introduced in: v20.1.0
Returns a value from a column at a specified offset from the current row.
This function is deprecated and error-prone because it operates on the physical order of data blocks which may not correspond to the logical order expected by users.
Consider using proper window functions instead.
The function can be enabled by setting
allow_deprecated_error_prone_window_functions = 1
.
Syntax
neighbor(column, offset[, default_value])
Arguments
column
β The source column.
Any
offset
β The offset from the current row. Positive values look forward, negative values look backward.
Integer
default_value
β Optional. The value to return if the offset goes beyond the data bounds. If not specified, uses the default value for the column type.
Any
Returned value
Returns a value from the specified offset, or default if out of bounds.
Any
Examples
Usage example
SELECT number, neighbor(number, 2) FROM system.numbers LIMIT 10;
ββnumberββ¬βneighbor(number, 2)ββ
β 0 β 2 β
β 1 β 3 β
β 2 β 4 β
β 3 β 5 β
β 4 β 6 β
β 5 β 7 β
β 6 β 8 β
β 7 β 9 β
β 8 β 0 β
β 9 β 0 β
ββββββββββ΄ββββββββββββββββββββββ
With default value
SELECT number, neighbor(number, 2, 999) FROM system.numbers LIMIT 10;
ββnumberββ¬βneighbor(number, 2, 999)ββ
β 0 β 2 β
β 1 β 3 β
β 2 β 4 β
β 3 β 5 β
β 4 β 6 β
β 5 β 7 β
β 6 β 8 β
β 7 β 9 β
β 8 β 999 β
β 9 β 999 β
ββββββββββ΄βββββββββββββββββββββββββββ
normalizeQuery
β
Introduced in: v20.8.0
Replaces literals, sequences of literals and complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with placeholder
?
.
Syntax
normalizeQuery(x)
Arguments
x
β Sequence of characters.
String
Returned value
Returns the given sequence of characters with placeholders.
String
Examples
Usage example
SELECT normalizeQuery('[1, 2, 3, x]') AS query
ββqueryβββββ
β [?.., x] β
ββββββββββββ
normalizeQueryKeepNames
β
Introduced in: v21.2.0
Replaces literals and sequences of literals with placeholder
?
but does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs).
This helps better analyze complex query logs.
Syntax
normalizeQueryKeepNames(x)
Arguments
x
β Sequence of characters.
String
Returned value
Returns the given sequence of characters with placeholders.
String
Examples
Usage example
SELECT normalizeQuery('SELECT 1 AS aComplexName123'), normalizeQueryKeepNames('SELECT 1 AS aComplexName123')
ββnormalizeQuery('SELECT 1 AS aComplexName123')ββ¬βnormalizeQueryKeepNames('SELECT 1 AS aComplexName123')ββ
β SELECT ? AS `?` β SELECT ? AS aComplexName123 β
βββββββββββββββββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
normalizedQueryHash
β
Introduced in: v20.8.0
Returns identical 64 bit hash values without the values of literals for similar queries.
Can be helpful in analyzing query logs.
Syntax
normalizedQueryHash(x)
Arguments
x
β Sequence of characters.
String
Returned value
Returns a 64 bit hash value.
UInt64
Examples
Usage example
SELECT normalizedQueryHash('SELECT 1 AS `xyz`') != normalizedQueryHash('SELECT 1 AS `abc`') AS res
ββresββ
β 1 β
βββββββ
normalizedQueryHashKeepNames
β
Introduced in: v21.2.0
Like
normalizedQueryHash
it returns identical 64 bit hash values without the values of literals for similar queries, but it does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with a placeholder before hashing.
Can be helpful in analyzing query logs.
Syntax
normalizedQueryHashKeepNames(x)
Arguments
x
β Sequence of characters.
String
Returned value
Returns a 64 bit hash value.
UInt64
Examples
Usage example
SELECT normalizedQueryHash('SELECT 1 AS `xyz123`') != normalizedQueryHash('SELECT 1 AS `abc123`') AS normalizedQueryHash;
SELECT normalizedQueryHashKeepNames('SELECT 1 AS `xyz123`') != normalizedQueryHashKeepNames('SELECT 1 AS `abc123`') AS normalizedQueryHashKeepNames;
ββnormalizedQueryHashββ
β 0 β
βββββββββββββββββββββββ
ββnormalizedQueryHashKeepNamesββ
β 1 β
ββββββββββββββββββββββββββββββββ
parseReadableSize
β
Introduced in: v24.6.0
Given a string containing a byte size and
B
,
KiB
,
KB
,
MiB
,
MB
, etc. as a unit (i.e.
ISO/IEC 80000-13
or decimal byte unit), this function returns the corresponding number of bytes.
If the function is unable to parse the input value, it throws an exception.
The inverse operations of this function are
formatReadableSize
and
formatReadableDecimalSize
.
Syntax
parseReadableSize(x)
Arguments
x
β Readable size with ISO/IEC 80000-13 or decimal byte unit.
String
Returned value
Returns the number of bytes, rounded up to the nearest integer.
UInt64
Examples
Usage example
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB']) AS readable_sizes, parseReadableSize(readable_sizes) AS sizes;
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
ββββββββββββββββββ΄ββββββββββ
parseReadableSizeOrNull
β
Introduced in: v24.6.0
Given a string containing a byte size and
B
,
KiB
,
KB
,
MiB
,
MB
, etc. as a unit (i.e.
ISO/IEC 80000-13
or decimal byte unit), this function returns the corresponding number of bytes.
If the function is unable to parse the input value, it returns
NULL
.
The inverse operations of this function are
formatReadableSize
and
formatReadableDecimalSize
.
Syntax
parseReadableSizeOrNull(x)
Arguments
x
β Readable size with ISO/IEC 80000-13 or decimal byte unit.
String
Returned value
Returns the number of bytes, rounded up to the nearest integer, or
NULL
if unable to parse the input
Nullable(UInt64)
Examples
Usage example
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB', 'invalid']) AS readable_sizes, parseReadableSizeOrNull(readable_sizes) AS sizes;
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
β invalid β α΄Ία΅α΄Έα΄Έ β
ββββββββββββββββββ΄ββββββββββ
parseReadableSizeOrZero
β
Introduced in: v24.6.0
Given a string containing a byte size and
B
,
KiB
,
KB
,
MiB
,
MB
, etc. as a unit (i.e.
ISO/IEC 80000-13
or decimal byte unit), this function returns the corresponding number of bytes.
If the function is unable to parse the input value, it returns
0
.
The inverse operations of this function are
formatReadableSize
and
formatReadableDecimalSize
.
Syntax
parseReadableSizeOrZero(x)
Arguments
x
β Readable size with ISO/IEC 80000-13 or decimal byte unit.
String
Returned value
Returns the number of bytes, rounded up to the nearest integer, or
0
if unable to parse the input.
UInt64
Examples
Usage example
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB', 'invalid']) AS readable_sizes, parseReadableSizeOrZero(readable_sizes) AS sizes;
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
β invalid β 0 β
ββββββββββββββββββ΄ββββββββββ
parseTimeDelta
β
Introduced in: v22.7.0
Parse a sequence of numbers followed by something resembling a time unit.
The time delta string uses these time unit specifications:
years
,
year
,
yr
,
y
months
,
month
,
mo
weeks
,
week
,
w
days
,
day
,
d
hours
,
hour
,
hr
,
h
minutes
,
minute
,
min
,
m
seconds
,
second
,
sec
,
s
milliseconds
,
millisecond
,
millisec
,
ms
microseconds
,
microsecond
,
microsec
,
ΞΌs
,
Β΅s
,
us
nanoseconds
,
nanosecond
,
nanosec
,
ns
Multiple time units can be combined with separators (space,
;
,
-
,
+
,
,
,
:
).
The length of years and months are approximations: year is 365 days, month is 30.5 days.
Syntax
parseTimeDelta(timestr)
Arguments
timestr
β A sequence of numbers followed by something resembling a time unit.
String
Returned value
The number of seconds.
Float64
Examples
Usage example
SELECT parseTimeDelta('11s+22min')
ββparseTimeDelta('11s+22min')ββ
β 1331 β
βββββββββββββββββββββββββββββββ
Complex time units
SELECT parseTimeDelta('1yr2mo')
ββparseTimeDelta('1yr2mo')ββ
β 36806400 β
ββββββββββββββββββββββββββββ
partitionId
β
Introduced in: v21.4.0
Computes the
partition ID
.
Note
This function is slow and should not be called for large numbers of rows.
Syntax
partitionId(column1[, column2, ...])
Aliases
:
partitionID
Arguments
column1, column2, ...
β Column for which to return the partition ID.
Returned value
Returns the partition ID that the row belongs to.
String
Examples
Usage example
DROP TABLE IF EXISTS tab;
CREATE TABLE tab
(
i int,
j int
)
ENGINE = MergeTree
PARTITION BY i
ORDER BY tuple();
INSERT INTO tab VALUES (1, 1), (1, 2), (1, 3), (2, 4), (2, 5), (2, 6);
SELECT i, j, partitionId(i), _partition_id FROM tab ORDER BY i, j;
ββiββ¬βjββ¬βpartitionId(i)ββ¬β_partition_idββ
β 1 β 1 β 1 β 1 β
β 1 β 2 β 1 β 1 β
β 1 β 3 β 1 β 1 β
β 2 β 4 β 2 β 2 β
β 2 β 5 β 2 β 2 β
β 2 β 6 β 2 β 2 β
βββββ΄ββββ΄βββββββββββββββββ΄ββββββββββββββββ
queryID
β
Introduced in: v21.9.0
Returns the ID of the current query.
Other parameters of a query can be extracted from field
query_id
in the
system.query_log
table.
In contrast to
initialQueryID
function,
queryID
can return different results on different shards.
Syntax
queryID()
Aliases
:
query_id
Arguments
None.
Returned value
Returns the ID of the current query.
String
Examples
Usage example
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT queryID() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
ββcount(DISTINCT t)ββ
β 3 β
βββββββββββββββββββββ
revision
β
Introduced in: v22.7.0
Returns the current ClickHouse server revision.
Syntax
revision()
Arguments
None.
Returned value
Returns the current ClickHouse server revision.
UInt32
Examples
Usage example
SELECT revision()
ββrevision()ββ
β 54485 β
ββββββββββββββ
rowNumberInAllBlocks
β
Introduced in: v1.1.0
Returns a unique row number for each row processed.
Syntax
rowNumberInAllBlocks()
Arguments
None.
Returned value
Returns the ordinal number of the row in the data block starting from
0
.
UInt64
Examples
Usage example
SELECT rowNumberInAllBlocks()
FROM
(
SELECT *
FROM system.numbers_mt
LIMIT 10
)
SETTINGS max_block_size = 2
ββrowNumberInAllBlocks()ββ
β 0 β
β 1 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 4 β
β 5 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 2 β
β 3 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 6 β
β 7 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 8 β
β 9 β
ββββββββββββββββββββββββββ
rowNumberInBlock
β
Introduced in: v1.1.0
For each
block
processed by
rowNumberInBlock
, returns the number of the current row.
The returned number starts from 0 for each block.
Syntax
rowNumberInBlock()
Arguments
None.
Returned value
Returns the ordinal number of the row in the data block starting from
0
.
UInt64
Examples
Usage example
SELECT rowNumberInBlock()
FROM
(
SELECT *
FROM system.numbers_mt
LIMIT 10
) SETTINGS max_block_size = 2
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
runningAccumulate
β
Introduced in: v1.1.0
Accumulates the states of an aggregate function for each row of a data block.
Syntax
runningAccumulate(agg_state[, grouping])
Arguments
agg_state
β State of the aggregate function.
AggregateFunction
grouping
β Optional. Grouping key. The state of the function is reset if the
grouping
value is changed. It can be any of the supported data types for which the equality operator is defined.
Any
Returned value
Returns the accumulated result for each row.
Any
Examples
Usage example with initializeAggregation
WITH initializeAggregation('sumState', number) AS one_row_sum_state
SELECT
number,
finalizeAggregation(one_row_sum_state) AS one_row_sum,
runningAccumulate(one_row_sum_state) AS cumulative_sum
FROM numbers(5);
ββnumberββ¬βone_row_sumββ¬βcumulative_sumββ
β 0 β 0 β 0 β
β 1 β 1 β 1 β
β 2 β 2 β 3 β
β 3 β 3 β 6 β
β 4 β 4 β 10 β
ββββββββββ΄ββββββββββββββ΄βββββββββββββββββ
runningConcurrency
β
Introduced in: v21.3.0
Calculates the number of concurrent events.
Each event has a start time and an end time.
The start time is included in the event, while the end time is excluded.
Columns with a start time and an end time must be of the same data type.
The function calculates the total number of active (concurrent) events for each event start time.
Requirements
Events must be ordered by the start time in ascending order.
If this requirement is violated the function raises an exception.
Every data block is processed separately.
If events from different data blocks overlap then they can not be processed correctly.
Syntax
runningConcurrency(start, end)
Arguments
start
β A column with the start time of events.
Date
or
DateTime
or
DateTime64
end
β A column with the end time of events.
Date
or
DateTime
or
DateTime64
Returned value
Returns the number of concurrent events at each event start time.
UInt32
Examples
Usage example
SELECT start, runningConcurrency(start, end) FROM example_table;
βββββββstartββ¬βrunningConcurrency(start, end)ββ
β 2025-03-03 β 1 β
β 2025-03-06 β 2 β
β 2025-03-07 β 3 β
β 2025-03-11 β 2 β
ββββββββββββββ΄βββββββββββββββββββββββββββββββββ
runningDifference
β
Introduced in: v1.1.0
Calculates the difference between two consecutive row values in the data block.
Returns
0
for the first row, and for subsequent rows the difference to the previous row.
The result of the function depends on the affected data blocks and the order of data in the block.
The order of rows during calculation of
runningDifference()
can differ from the order of rows returned to the user.
To prevent that you can create a subquery with
ORDER BY
and call the function from outside the subquery.
Please note that the block size affects the result.
The internal state of
runningDifference
state is reset for each new block.
Syntax
runningDifference(x)
Arguments
x
β Column for which to calculate the running difference.
Any
Returned value
Returns the difference between consecutive values, with 0 for the first row.
Examples
Usage example
SELECT
EventID,
EventTime,
runningDifference(EventTime) AS delta
FROM
(
SELECT
EventID,
EventTime
FROM events
WHERE EventDate = '2025-11-24'
ORDER BY EventTime ASC
LIMIT 5
);
ββEventIDββ¬βββββββββββEventTimeββ¬βdeltaββ
β 1106 β 2025-11-24 00:00:04 β 0 β
β 1107 β 2025-11-24 00:00:05 β 1 β
β 1108 β 2025-11-24 00:00:05 β 0 β
β 1109 β 2025-11-24 00:00:09 β 4 β
β 1110 β 2025-11-24 00:00:10 β 1 β
βββββββββββ΄ββββββββββββββββββββββ΄ββββββββ
Block size impact example
SELECT
number,
runningDifference(number + 1) AS diff
FROM numbers(100000)
WHERE diff != 1;
ββnumberββ¬βdiffββ
β 0 β 0 β
ββββββββββ΄βββββββ
ββnumberββ¬βdiffββ
β 65536 β 0 β
ββββββββββ΄βββββββ
runningDifferenceStartingWithFirstValue
β
Introduced in: v1.1.0
Calculates the difference between consecutive row values in a data block, but unlike
runningDifference
, it returns the actual value of the first row instead of
0
.
Deprecated
Only returns differences inside the currently processed data block.
Because of this error-prone behavior, the function is deprecated.
It is advised to use
window functions
instead.
You can use setting
allow_deprecated_error_prone_window_functions
to allow usage of this function.
Syntax
runningDifferenceStartingWithFirstValue(x)
Arguments
x
β Column for which to calculate the running difference.
Any
Returned value
Returns the difference between consecutive values, with the first row's value for the first row.
Any
Examples
Usage example
SELECT
number,
runningDifferenceStartingWithFirstValue(number) AS diff
FROM numbers(5);
ββnumberββ¬βdiffββ
β 0 β 0 β
β 1 β 1 β
β 2 β 1 β
β 3 β 1 β
β 4 β 1 β
ββββββββββ΄βββββββ
serverUUID
β
Introduced in: v20.1.0
Returns the random and unique UUID (v4) generated when the server is first started.
The UUID is persisted, i.e. the second, third, etc. server start return the same UUID.
Syntax
serverUUID()
Arguments
None.
Returned value
Returns the random UUID of the server.
UUID
Examples
Usage example
SELECT serverUUID();
ββserverUUID()ββββββββββββββββββββββββββββββ
β 7ccc9260-000d-4d5c-a843-5459abaabb5f β
ββββββββββββββββββββββββββββββββββββββββββββ
shardCount
β
Introduced in: v21.9.0
Returns the total number of shards for a distributed query.
If a query is not distributed then constant value
0
is returned.
Syntax
shardCount()
Arguments
None.
Returned value
Returns the total number of shards or
0
.
UInt32
Examples
Usage example
-- See shardNum() example above which also demonstrates shardCount()
CREATE TABLE shard_count_example (dummy UInt8)
ENGINE=Distributed(test_cluster_two_shards_localhost, system, one, dummy);
SELECT shardCount() FROM shard_count_example;
ββshardCount()ββ
β 2 β
β 2 β
ββββββββββββββββ
shardNum
β
Introduced in: v21.9.0
Returns the index of a shard which processes a part of data in a distributed query.
Indices begin from
1
.
If a query is not distributed then a constant value
0
is returned.
Syntax
shardNum()
Arguments
None.
Returned value
Returns the shard index or a constant
0
.
UInt32
Examples
Usage example
CREATE TABLE shard_num_example (dummy UInt8)
ENGINE=Distributed(test_cluster_two_shards_localhost, system, one, dummy);
SELECT dummy, shardNum(), shardCount() FROM shard_num_example;
ββdummyββ¬βshardNum()ββ¬βshardCount()ββ
β 0 β 1 β 2 β
β 0 β 2 β 2 β
βββββββββ΄βββββββββββββ΄βββββββββββββββ
showCertificate
β
Introduced in: v22.6.0
Shows information about the current server's Secure Sockets Layer (SSL) certificate if it has been configured.
See
Configuring TLS
for more information on how to configure ClickHouse to use OpenSSL certificates to validate connections.
Syntax
showCertificate()
Arguments
None.
Returned value
Returns map of key-value pairs relating to the configured SSL certificate.
Map(String, String)
Examples
Usage example
SELECT showCertificate() FORMAT LineAsString;
{'version':'1','serial_number':'2D9071D64530052D48308473922C7ADAFA85D6C5','signature_algo':'sha256WithRSAEncryption','issuer':'/CN=marsnet.local CA','not_before':'May 7 17:01:21 2024 GMT','not_after':'May 7 17:01:21 2025 GMT','subject':'/CN=chnode1','pkey_algo':'rsaEncryption'}
sleep
β
Introduced in: v1.1.0
Pauses the execution of a query by the specified number of seconds.
The function is primarily used for testing and debugging purposes.
The
sleep()
function should generally not be used in production environments, as it can negatively impact query performance and system responsiveness.
However, it can be useful in the following scenarios:
Testing
: When testing or benchmarking ClickHouse, you may want to simulate delays or introduce pauses to observe how the system behaves under certain conditions.
Debugging
: If you need to examine the state of the system or the execution of a query at a specific point in time, you can use
sleep()
to introduce a pause, allowing you to inspect or collect relevant information.
Simulation
: In some cases, you may want to simulate real-world scenarios where delays or pauses occur, such as network latency or external system dependencies.
Note
It's important to use the
sleep()
function judiciously and only when necessary, as it can potentially impact the overall performance and responsiveness of your ClickHouse system.
For security reasons, the function can only be executed in the default user profile (with
allow_sleep
enabled).
Syntax
sleep(seconds)
Arguments
seconds
β The number of seconds to pause the query execution to a maximum of 3 seconds. It can be a floating-point value to specify fractional seconds.
const UInt*
or
const Float*
Returned value
Returns
0
.
UInt8
Examples
Usage example
-- This query will pause for 2 seconds before completing.
-- During this time, no results will be returned, and the query will appear to be hanging or unresponsive.
SELECT sleep(2);
ββsleep(2)ββ
β 0 β
ββββββββββββ
1 row in set. Elapsed: 2.012 sec.
sleepEachRow
β
Introduced in: v1.1.0
Pauses the execution of a query for a specified number of seconds for each row in the result set.
The
sleepEachRow()
function is primarily used for testing and debugging purposes, similar to the
sleep()
function.
It allows you to simulate delays or introduce pauses in the processing of each row, which can be useful in scenarios such as:
Testing
: When testing or benchmarking ClickHouse's performance under specific conditions, you can use
sleepEachRow()
to simulate delays or introduce pauses for each row processed.
Debugging
: If you need to examine the state of the system or the execution of a query for each row processed, you can use
sleepEachRow()
to introduce pauses, allowing you to inspect or collect relevant information.
Simulation
: In some cases, you may want to simulate real-world scenarios where delays or pauses occur for each row processed, such as when dealing with external systems or network latencies.
Note
Like the
sleep()
function, it's important to use
sleepEachRow()
judiciously and only when necessary, as it can significantly impact the overall performance and responsiveness of your ClickHouse system, especially when dealing with large result sets.
Syntax
sleepEachRow(seconds)
Arguments
seconds
β The number of seconds to pause the query execution for each row in the result set to a maximum of 3 seconds. It can be a floating-point value to specify fractional seconds.
const UInt*
or
const Float*
Returned value
Returns
0
for each row.
UInt8
Examples
Usage example
-- The output will be delayed, with a 0.5-second pause between each row.
SELECT number, sleepEachRow(0.5) FROM system.numbers LIMIT 5;
ββnumberββ¬βsleepEachRow(0.5)ββ
β 0 β 0 β
β 1 β 0 β
β 2 β 0 β
β 3 β 0 β
β 4 β 0 β
ββββββββββ΄ββββββββββββββββββββ
structureToCapnProtoSchema
β
Introduced in: v23.8.0
Function that converts ClickHouse table structure to CapnProto format schema
Syntax
structureToCapnProtoSchema(table_structure, message)
Arguments
None.
Returned value
Examples
random
SELECT structureToCapnProtoSchema('s String, x UInt32', 'MessageName') format TSVRaw
struct MessageName
{
s @0 : Data;
x @1 : UInt32;
}
structureToProtobufSchema
β
Introduced in: v23.8.0
Converts a ClickHouse table structure to Protobuf format schema.
This function takes a ClickHouse table structure definition and converts it into a Protocol Buffers (Protobuf)
schema definition in proto3 syntax. This is useful for generating Protobuf schemas that match your ClickHouse
table structures for data interchange.
Syntax
structureToProtobufSchema(structure, message_name)
Arguments
structure
β ClickHouse table structure definition as a string (e.g., 'column1 Type1, column2 Type2').
String
message_name
β Name for the Protobuf message type in the generated schema.
String
Returned value
Returns a Protobuf schema definition in proto3 syntax that corresponds to the input ClickHouse structure.
String
Examples
Converting ClickHouse structure to Protobuf schema
SELECT structureToProtobufSchema('s String, x UInt32', 'MessageName') FORMAT TSVRaw;
syntax = "proto3";
message MessageName
{
bytes s = 1;
uint32 x = 2;
}
tcpPort
β
Introduced in: v20.12.0
Returns the
native interface
TCP port number listened to by the server.
If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard.
Otherwise it produces a constant value.
Syntax
tcpPort()
Arguments
None.
Returned value
Returns the TCP port number.
UInt16
Examples
Usage example
SELECT tcpPort()
ββtcpPort()ββ
β 9000 β
βββββββββββββ
throwIf
β
Introduced in: v1.1.0
Throw an exception if argument x is true.
To use the
error_code
argument, configuration parameter
allow_custom_error_code_in_throw
must be enabled.
Syntax
throwIf(x[, message[, error_code]])
Arguments
x
β The condition to check.
Any
message
β Optional. Custom error message.
const String
error_code
β Optional. Custom error code.
const Int8/16/32
Returned value
Returns
0
if the condition is false, throws an exception if the condition is true.
UInt8
Examples
Usage example
SELECT throwIf(number = 3, 'Too many') FROM numbers(10);
β Progress: 0.00 rows, 0.00 B (0.00 rows/s., 0.00 B/s.) Received exception from server (version 19.14.1):
Code: 395. DB::Exception: Received from localhost:9000. DB::Exception: Too many.
toColumnTypeName
β
Introduced in: v1.1.0
Returns the internal name of the data type of the given value.
Unlike function
toTypeName
, the returned data type potentially includes internal wrapper columns like
Const
and
LowCardinality
.
Syntax
toColumnTypeName(value)
Arguments
value
β Value for which to return the internal data type.
Any
Returned value
Returns the internal data type used to represent the value.
String
Examples
Usage example
SELECT toColumnTypeName(CAST('2025-01-01 01:02:03' AS DateTime));
ββtoColumnTypeName(CAST('2025-01-01 01:02:03', 'DateTime'))ββ
β Const(UInt32) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
toTypeName
β
Introduced in: v1.1.0
Returns the type name of the passed argument.
If
NULL
is passed, the function returns type
Nullable(Nothing)
, which corresponds to ClickHouse's internal
NULL
representation.
Syntax
toTypeName(x)
Arguments
x
β A value of arbitrary type.
Any
Returned value
Returns the data type name of the input value.
String
Examples
Usage example
SELECT toTypeName(123)
ββtoTypeName(123)ββ
β UInt8 β
βββββββββββββββββββ
transactionID
β
Introduced in: v22.6.0
Not supported in ClickHouse Cloud
Returns the ID of a transaction.
Note
This function is part of an experimental feature set.
Enable experimental transaction support by adding this setting to your
configuration
:
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
For more information see the page
Transactional (ACID) support
.
Syntax
transactionID()
Arguments
None.
Returned value
Returns a tuple consisting of
start_csn
,
local_tid
and
host_id
.
start_csn
: Global sequential number, the newest commit timestamp that was seen when this transaction began.
local_tid
: Local sequential number that is unique for each transaction started by this host within a specific start_csn.
host_id
: UUID of the host that has started this transaction.
Tuple(UInt64, UInt64, UUID)
Examples
Usage example
BEGIN TRANSACTION;
SELECT transactionID();
ROLLBACK;
ββtransactionID()βββββββββββββββββββββββββββββββββ
β (32,34,'0ee8b069-f2bb-4748-9eae-069c85b5252b') β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
transactionLatestSnapshot
β
Introduced in: v22.6.0
Not supported in ClickHouse Cloud
Returns the newest snapshot (Commit Sequence Number) of a
transaction
that is available for reading.
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your configuration:
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
For more information see the page
Transactional (ACID) support
.
Syntax
transactionLatestSnapshot()
Arguments
None.
Returned value
Returns the latest snapshot (CSN) of a transaction.
UInt64
Examples
Usage example
BEGIN TRANSACTION;
SELECT transactionLatestSnapshot();
ROLLBACK;
ββtransactionLatestSnapshot()ββ
β 32 β
βββββββββββββββββββββββββββββββ
transactionOldestSnapshot
β
Introduced in: v22.6.0
Not supported in ClickHouse Cloud
Returns the oldest snapshot (Commit Sequence Number) that is visible for some running
transaction
.
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your configuration:
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
For more information see the page
Transactional (ACID) support
.
Syntax
transactionOldestSnapshot()
Arguments
None.
Returned value
Returns the oldest snapshot (CSN) of a transaction.
UInt64
Examples
Usage example
BEGIN TRANSACTION;
SELECT transactionOldestSnapshot();
ROLLBACK;
ββtransactionOldestSnapshot()ββ
β 32 β
βββββββββββββββββββββββββββββββ
transform
β
Introduced in: v1.1.0
Transforms a value according to the explicitly defined mapping of some elements to other elements.
There are two variations of this function:
transform(x, array_from, array_to, default)
- transforms
x
using mapping arrays with a default value for unmatched elements
transform(x, array_from, array_to)
- same transformation but returns the original
x
if no match is found
The function searches for
x
in
array_from
and returns the corresponding element from
array_to
at the same index.
If
x
is not found in
array_from
, it returns either the
default
value (4-parameter version) or the original
x
(3-parameter version).
If multiple matching elements exist in
array_from
, it returns the element corresponding to the first match.
Requirements:
array_from
and
array_to
must have the same number of elements
For 4-parameter version:
transform(T, Array(T), Array(U), U) -> U
where
T
and
U
can be different compatible types
For 3-parameter version:
transform(T, Array(T), Array(T)) -> T
where all types must be the same
Syntax
transform(x, array_from, array_to[, default])
Arguments
x
β Value to transform.
(U)Int*
or
Decimal
or
Float*
or
String
or
Date
or
DateTime
array_from
β Constant array of values to search for matches.
Array((U)Int*)
or
Array(Decimal)
or
Array(Float*)
or
Array(String)
or
Array(Date)
or
Array(DateTime)
array_to
β Constant array of values to return for corresponding matches in
array_from
.
Array((U)Int*)
or
Array(Decimal)
or
Array(Float*)
or
Array(String)
or
Array(Date)
or
Array(DateTime)
default
β Optional. Value to return if
x
is not found in
array_from
. If omitted, returns x unchanged.
(U)Int*
or
Decimal
or
Float*
or
String
or
Date
or
DateTime
Returned value
Returns the corresponding value from
array_to
if x matches an element in
array_from
, otherwise returns default (if provided) or x (if default not provided).
Any
Examples
transform(T, Array(T), Array(U), U) -> U
SELECT
transform(SearchEngineID, [2, 3], ['Yandex', 'Google'], 'Other') AS title,
count() AS c
FROM test.hits
WHERE SearchEngineID != 0
GROUP BY title
ORDER BY c DESC
ββtitleββββββ¬ββββββcββ
β Yandex β 498635 β
β Google β 229872 β
β Other β 104472 β
βββββββββββββ΄βββββββββ
transform(T, Array(T), Array(T)) -> T
SELECT
transform(domain(Referer), ['yandex.ru', 'google.ru', 'vkontakte.ru'], ['www.yandex', 'example.com', 'vk.com']) AS s, count() AS c
FROM test.hits
GROUP BY domain(Referer)
ORDER BY count() DESC
LIMIT 10
ββsβββββββββββββββ¬βββββββcββ
β β 2906259 β
β www.yandex β 867767 β
β βββββββ.ru β 313599 β
β mail.yandex.ru β 107147 β
β ββββββ.ru β 100355 β
β βββββββββ.ru β 65040 β
β news.yandex.ru β 64515 β
β ββββββ.net β 59141 β
β example.com β 57316 β
ββββββββββββββββββ΄ββββββββββ
uniqThetaIntersect
β
Introduced in: v22.9.0
Two uniqThetaSketch objects to do intersect calculation(set operation β©), the result is a new uniqThetaSketch.
Syntax
uniqThetaIntersect(uniqThetaSketch,uniqThetaSketch)
Arguments
uniqThetaSketch
β uniqThetaSketch object.
Tuple
or
Array
or
Date
or
DateTime
or
String
or
(U)Int*
or
Float*
or
Decimal
Returned value
A new uniqThetaSketch containing the intersect result.
UInt64
Examples
Usage example
SELECT finalizeAggregation(uniqThetaIntersect(a, b)) AS a_intersect_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [1, 2]) AS a, arrayReduce('uniqThetaState', [2, 3, 4]) AS b);
ββa_intersect_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 1 β 2 β 3 β
βββββββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
uniqThetaNot
β
Introduced in: v22.9.0
Two uniqThetaSketch objects to do a_not_b calculation(set operation Γ), the result is a new uniqThetaSketch.
Syntax
uniqThetaNot(uniqThetaSketch,uniqThetaSketch)
Arguments
uniqThetaSketch
β uniqThetaSketch object.
Tuple
or
Array
or
Date
or
DateTime
or
String
or
(U)Int*
or
Float*
or
Decimal
Returned value
Returns a new uniqThetaSketch containing the a_not_b result.
UInt64
Examples
Usage example
SELECT finalizeAggregation(uniqThetaNot(a, b)) AS a_not_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [2, 3, 4]) AS a, arrayReduce('uniqThetaState', [1, 2]) AS b);
ββa_not_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 2 β 3 β 2 β
βββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
uniqThetaUnion
β
Introduced in: v22.9.0
Two uniqThetaSketch objects to do union calculation(set operation βͺ), the result is a new uniqThetaSketch.
Syntax
uniqThetaUnion(uniqThetaSketch,uniqThetaSketch)
Arguments
uniqThetaSketch
β uniqThetaSketch object.
Tuple
or
Array
or
Date
or
DateTime
or
String
or
(U)Int*
or
Float*
or
Decimal
Returned value
Returns a new uniqThetaSketch containing the union result.
UInt64
Examples
Usage example
SELECT finalizeAggregation(uniqThetaUnion(a, b)) AS a_union_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [1, 2]) AS a, arrayReduce('uniqThetaState', [2, 3, 4]) AS b);
ββa_union_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 4 β 2 β 3 β
βββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
uptime
β
Introduced in: v1.1.0
Returns the server's uptime in seconds.
If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard.
Otherwise it produces a constant value.
Syntax
uptime()
Arguments
None.
Returned value
Returns the server uptime in seconds.
UInt32
Examples
Usage example
SELECT uptime() AS Uptime
ββUptimeββ
β 55867 β
ββββββββββ
variantElement
β
Introduced in: v25.2.0
Extracts a column with specified type from a
Variant
column.
Syntax
variantElement(variant, type_name[, default_value])
Arguments
variant
β Variant column.
Variant
type_name
β The name of the variant type to extract.
String
default_value
β The default value that will be used if variant doesn't have variant with specified type. Can be any type. Optional.
Any
Returned value
Returns a column with the specified variant type extracted from the Variant column.
Any
Examples
Usage example
CREATE TABLE test (v Variant(UInt64, String, Array(UInt64))) ENGINE = Memory;
INSERT INTO test VALUES (NULL), (42), ('Hello, World!'), ([1, 2, 3]);
SELECT v, variantElement(v, 'String'), variantElement(v, 'UInt64'), variantElement(v, 'Array(UInt64)') FROM test;
ββvββββββββββββββ¬βvariantElement(v, 'String')ββ¬βvariantElement(v, 'UInt64')ββ¬βvariantElement(v, 'Array(UInt64)')ββ
β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β [] β
β 42 β α΄Ία΅α΄Έα΄Έ β 42 β [] β
β Hello, World! β Hello, World! β α΄Ία΅α΄Έα΄Έ β [] β
β [1,2,3] β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β [1,2,3] β
βββββββββββββββββ΄ββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββ
variantType
β
Introduced in: v24.2.0
Returns the variant type name for each row of
Variant
column. If row contains NULL, it returns 'None' for it.
Syntax
variantType(variant)
Arguments
variant
β Variant column.
Variant
Returned value
Returns an Enum column with variant type name for each row.
Enum
Examples
Usage example
CREATE TABLE test (v Variant(UInt64, String, Array(UInt64))) ENGINE = Memory;
INSERT INTO test VALUES (NULL), (42), ('Hello, World!'), ([1, 2, 3]);
SELECT variantType(v) FROM test;
ββvariantType(v)ββ
β None β
β UInt64 β
β String β
β Array(UInt64) β
ββββββββββββββββββ
version
β
Introduced in: v1.1.0
Returns the current version of ClickHouse as a string in the form:
major_version.minor_version.patch_version.number_of_commits_since_the_previous_stable_release
.
If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard.
Otherwise, it produces a constant value.
Syntax
version()
Arguments
None.
Returned value
Returns the current version of ClickHouse.
String
Examples
Usage example
SELECT version()
ββversion()ββ
β 24.2.1.1 β
βββββββββββββ
visibleWidth
β
Introduced in: v1.1.0
Calculates the approximate width when outputting values to the console in text format (tab-separated).
This function is used by the system to implement Pretty formats.
NULL
is represented as a string corresponding to
NULL
in Pretty formats.
Syntax
visibleWidth(x)
Arguments
x
β A value of any data type.
Any
Returned value
Returns the approximate width of the value when displayed in text format.
UInt64
Examples
Calculate visible width of NULL
SELECT visibleWidth(NULL)
ββvisibleWidth(NULL)ββ
β 4 β
ββββββββββββββββββββββ
zookeeperSessionUptime
β
Introduced in: v21.11.0
Returns the uptime of the current ZooKeeper session in seconds.
Syntax
zookeeperSessionUptime()
Arguments
None.
Returned value
Returns the uptime of the current ZooKeeper session in seconds.
UInt32
Examples
Usage example
SELECT zookeeperSessionUptime();
ββzookeeperSessionUptime()ββ
β 286 β
ββββββββββββββββββββββββββββ |
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- [Overview](https://clickhouse.com/docs/sql-reference/functions/overview)
- [AI](https://clickhouse.com/docs/sql-reference/functions/ai-functions)
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- [Comparison](https://clickhouse.com/docs/sql-reference/functions/comparison-functions)
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- [Dates and time](https://clickhouse.com/docs/sql-reference/functions/date-time-functions)
- [Distance](https://clickhouse.com/docs/sql-reference/functions/distance-functions)
- [Embedded dictionary](https://clickhouse.com/docs/sql-reference/functions/ym-dict-functions)
- [Encoding](https://clickhouse.com/docs/sql-reference/functions/encoding-functions)
- [Encryption](https://clickhouse.com/docs/sql-reference/functions/encryption-functions)
- [Dictionaries](https://clickhouse.com/docs/sql-reference/functions/ext-dict-functions)
- [Files](https://clickhouse.com/docs/sql-reference/functions/files)
- [Financial](https://clickhouse.com/docs/sql-reference/functions/financial-functions)
- [Nullable](https://clickhouse.com/docs/sql-reference/functions/functions-for-nulls)
- [Geometry](https://clickhouse.com/docs/sql-reference/functions/geo)
- [Hash](https://clickhouse.com/docs/sql-reference/functions/hash-functions)
- [IN Operator](https://clickhouse.com/docs/sql-reference/functions/in-functions)
- [Introspection](https://clickhouse.com/docs/sql-reference/functions/introspection)
- [IP Addresses](https://clickhouse.com/docs/sql-reference/functions/ip-address-functions)
- [JSON](https://clickhouse.com/docs/sql-reference/functions/json-functions)
- [Logical](https://clickhouse.com/docs/sql-reference/functions/logical-functions)
- [Machine Learning](https://clickhouse.com/docs/sql-reference/functions/machine-learning-functions)
- [Mathematical](https://clickhouse.com/docs/sql-reference/functions/math-functions)
- [NLP](https://clickhouse.com/docs/sql-reference/functions/nlp-functions)
- [NumericIndexedVector](https://clickhouse.com/docs/sql-reference/functions/numeric-indexed-vector-functions)
- [Other](https://clickhouse.com/docs/sql-reference/functions/other-functions)
- [Random number](https://clickhouse.com/docs/sql-reference/functions/random-functions)
- [Rounding](https://clickhouse.com/docs/sql-reference/functions/rounding-functions)
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- [Data Lakes](https://clickhouse.com/docs/sql-reference/datalakes)
- [Functions](https://clickhouse.com/docs/sql-reference/functions)
- [Regular functions](https://clickhouse.com/docs/sql-reference/functions/regular-functions)
- Other
[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/sql-reference/functions/other-functions.md)
# Other functions
Note
The function documentation below is generated from the `system.functions` system table.
## FQDN[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#FQDN "Direct link to FQDN")
Introduced in: v20.1.0
Returns the fully qualified domain name of the ClickHouse server.
**Syntax**
```
FQDN()
```
**Aliases**: `fullHostName`
**Arguments**
- None.
**Returned value**
Returns the fully qualified domain name of the ClickHouse server. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT fqdn()
```
Response
```
ββFQDN()βββββββββββββββββββββββββββ
β clickhouse.us-east-2.internal β
βββββββββββββββββββββββββββββββββββ
```
## MACNumToString[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACNumToString "Direct link to MACNumToString")
Introduced in: v1.1.0
Interprets a [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) number as a MAC address in big endian format. Returns the corresponding MAC address in format `AA:BB:CC:DD:EE:FF` (colon-separated numbers in hexadecimal form) as string.
**Syntax**
```
MACNumToString(num)
```
**Arguments**
- `num` β UInt64 number. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a MAC address in format AA:BB:CC:DD:EE:FF. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT MACNumToString(149809441867716) AS mac_address;
```
Response
```
ββmac_addressββββββββ
β 88:00:11:22:33:44 β
βββββββββββββββββββββ
```
## MACStringToNum[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACStringToNum "Direct link to MACStringToNum")
Introduced in: v1.1.0
The inverse function of MACNumToString. If the MAC address has an invalid format, it returns 0.
**Syntax**
```
MACStringToNum(s)
```
**Arguments**
- `s` β MAC address string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a UInt64 number. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT MACStringToNum('01:02:03:04:05:06') AS mac_numeric;
```
Response
```
1108152157446
```
## MACStringToOUI[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACStringToOUI "Direct link to MACStringToOUI")
Introduced in: v1.1.0
Given a MAC address in format AA:BB:CC:DD:EE:FF (colon-separated numbers in hexadecimal form), returns the first three octets as a UInt64 number. If the MAC address has an invalid format, it returns 0.
**Syntax**
```
MACStringToOUI(s)
```
**Arguments**
- `s` β MAC address string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
First three octets as UInt64 number. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT MACStringToOUI('00:50:56:12:34:56') AS oui;
```
Response
```
20566
```
## authenticatedUser[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#authenticatedUser "Direct link to authenticatedUser")
Introduced in: v25.11.0
If the session user has been switched using the EXECUTE AS command, this function returns the name of the original user that was used for authentication and creating the session. Alias: authUser()
**Syntax**
```
authenticatedUser()
```
**Aliases**: `authUser`
**Arguments**
- None.
**Returned value**
The name of the authenticated user. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
EXECUTE as u1;
SELECT currentUser(), authenticatedUser();
```
Response
```
ββcurrentUser()ββ¬βauthenticatedUser()ββ
β u1 β default β
βββββββββββββββββ΄ββββββββββββββββββββββ
```
## bar[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#bar "Direct link to bar")
Introduced in: v1.1.0
Builds a bar chart. Draws a band with width proportional to (x - min) and equal to width characters when x = max. The band is drawn with accuracy to one eighth of a symbol.
**Syntax**
```
bar(x, min, max[, width])
```
**Arguments**
- `x` β Size to display. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `min` β The minimum value. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `max` β The maximum value. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `width` β Optional. The width of the bar in characters. The default is `80`. [`const (U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`const Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`const Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns a unicode-art bar string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT
toHour(EventTime) AS h,
count() AS c,
bar(c, 0, 600000, 20) AS bar
FROM test.hits
GROUP BY h
ORDER BY h ASC
```
Response
```
βββhββ¬ββββββcββ¬βbarβββββββββββββββββ
β 0 β 292907 β ββββββββββ β
β 1 β 180563 β ββββββ β
β 2 β 114861 β ββββ β
β 3 β 85069 β βββ β
β 4 β 68543 β βββ β
β 5 β 78116 β βββ β
β 6 β 113474 β ββββ β
β 7 β 170678 β ββββββ β
β 8 β 278380 β ββββββββββ β
β 9 β 391053 β βββββββββββββ β
β 10 β 457681 β ββββββββββββββββ β
β 11 β 493667 β βββββββββββββββββ β
β 12 β 509641 β βββββββββββββββββ β
β 13 β 522947 β ββββββββββββββββββ β
β 14 β 539954 β ββββββββββββββββββ β
β 15 β 528460 β ββββββββββββββββββ β
β 16 β 539201 β ββββββββββββββββββ β
β 17 β 523539 β ββββββββββββββββββ β
β 18 β 506467 β βββββββββββββββββ β
β 19 β 520915 β ββββββββββββββββββ β
β 20 β 521665 β ββββββββββββββββββ β
β 21 β 542078 β ββββββββββββββββββ β
β 22 β 493642 β βββββββββββββββββ β
β 23 β 400397 β ββββββββββββββ β
ββββββ΄βββββββββ΄βββββββββββββββββββββ
```
## blockNumber[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockNumber "Direct link to blockNumber")
Introduced in: v1.1.0
Returns a monotonically increasing sequence number of the [block](https://clickhouse.com/docs/development/architecture#block) containing the row. The returned block number is updated on a best-effort basis, i.e. it may not be fully accurate.
**Syntax**
```
blockNumber()
```
**Arguments**
- None.
**Returned value**
Sequence number of the data block where the row is located. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Basic usage**
Query
```
SELECT blockNumber()
FROM
(
SELECT *
FROM system.numbers
LIMIT 10
) SETTINGS max_block_size = 2
```
Response
```
ββblockNumber()ββ
β 7 β
β 7 β
βββββββββββββββββ
ββblockNumber()ββ
β 8 β
β 8 β
βββββββββββββββββ
ββblockNumber()ββ
β 9 β
β 9 β
βββββββββββββββββ
ββblockNumber()ββ
β 10 β
β 10 β
βββββββββββββββββ
ββblockNumber()ββ
β 11 β
β 11 β
βββββββββββββββββ
```
## blockSerializedSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockSerializedSize "Direct link to blockSerializedSize")
Introduced in: v20.3.0
Returns the uncompressed size in bytes of a block of values on disk.
**Syntax**
```
blockSerializedSize(x1[, x2[, ...]])
```
**Arguments**
- `x1[, x2, ...]` β Any number of values for which to get the uncompressed size of the block. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the number of bytes that will be written to disk for a block of values without compression. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT blockSerializedSize(maxState(1)) AS x;
```
Response
```
ββxββ
β 2 β
βββββ
```
## blockSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockSize "Direct link to blockSize")
Introduced in: v1.1.0
In ClickHouse, queries are processed in [blocks](https://clickhouse.com/docs/development/architecture#block) (chunks). This function returns the size (row count) of the block the function is called on.
**Syntax**
```
blockSize()
```
**Arguments**
- None.
**Returned value**
Returns the number of rows in the current block. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT blockSize()
FROM system.numbers LIMIT 5
```
Response
```
ββblockSize()ββ
β 5 β
β 5 β
β 5 β
β 5 β
β 5 β
βββββββββββββββ
```
## buildId[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#buildId "Direct link to buildId")
Introduced in: v20.5.0
Returns the build ID generated by a compiler for the running ClickHouse server binary. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
buildId()
```
**Arguments**
- None.
**Returned value**
Returns the build ID. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT buildId()
```
Response
```
ββbuildId()βββββββββββββββββββββββββββββββββ
β AB668BEF095FAA6BD26537F197AC2AF48A927FB4 β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## byteSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#byteSize "Direct link to byteSize")
Introduced in: v21.1.0
Returns an estimation of the uncompressed byte size of its arguments in memory. For `String` arguments, the function returns the string length + 8 (length). If the function has multiple arguments, the function accumulates their byte sizes.
**Syntax**
```
byteSize(arg1[, arg2, ...])
```
**Arguments**
- `arg1[, arg2, ...]` β Values of any data type for which to estimate the uncompressed byte size. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns an estimation of the byte size of the arguments in memory. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT byteSize('string')
```
Response
```
ββbyteSize('string')ββ
β 15 β
ββββββββββββββββββββββ
```
**Multiple arguments**
Query
```
SELECT byteSize(NULL, 1, 0.3, '')
```
Response
```
ββbyteSize(NULL, 1, 0.3, '')ββ
β 19 β
ββββββββββββββββββββββββββββββ
```
## catboostEvaluate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#catboostEvaluate "Direct link to catboostEvaluate")
Introduced in: v22.9.0
Evaluate an external catboost model. [CatBoost](https://catboost.ai/) is an open-source gradient boosting library developed by Yandex for machine learning. Accepts a path to a catboost model and model arguments (features).
**Prerequisites**
1. Build the catboost evaluation library
Before evaluating catboost models, the `libcatboostmodel.<so|dylib>` library must be made available. See [CatBoost documentation](https://catboost.ai/docs/concepts/c-plus-plus-api_dynamic-c-pluplus-wrapper.html) how to compile it.
Next, specify the path to `libcatboostmodel.<so|dylib>` in the clickhouse configuration:
```
<clickhouse>
...
<catboost_lib_path>/path/to/libcatboostmodel.so</catboost_lib_path>
...
</clickhouse>
```
For security and isolation reasons, the model evaluation does not run in the server process but in the clickhouse-library-bridge process. At the first execution of `catboostEvaluate()`, the server starts the library bridge process if it is not running already. Both processes communicate using a HTTP interface. By default, port `9012` is used. A different port can be specified as follows - this is useful if port `9012` is already assigned to a different service.
```
<library_bridge>
<port>9019</port>
</library_bridge>
```
1. Train a catboost model using libcatboost
See [Training and applying models](https://catboost.ai/docs/features/training.html#training) for how to train catboost models from a training data set.
**Syntax**
```
catboostEvaluate(path_to_model, feature_1[, feature_2, ..., feature_n])
```
**Arguments**
- `path_to_model` β Path to catboost model. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `feature` β One or more model features/arguments. [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns the model evaluation result. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Examples**
**catboostEvaluate**
Query
```
SELECT catboostEvaluate('/root/occupy.bin', Temperature, Humidity, Light, CO2, HumidityRatio) AS prediction FROM occupancy LIMIT 1
```
Response
```
4.695691092573497
```
## colorOKLABToSRGB[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorOKLABToSRGB "Direct link to colorOKLABToSRGB")
Introduced in: v26.2.0
Converts a color from the OKLab perceptual color space to the sRGB color space.
The input color is specified in the OKLab color space. If the input values are outside the typical OKLab ranges, the result is implementation-defined.
OKLab uses three components:
- L: perceptual lightness (typically in the range \[0..1\])
- a: green-red opponent axis
- b: blue-yellow opponent axis
The a and b components are theoretically unbounded, but in practice are between -0.4 and 0.4. OKLab is designed to be perceptually uniform while remaining inexpensive to compute.
The conversion is intended to be the inverse of colorSRGBToOKLAB and consists of the following stages:
1. Conversion from OKLab to linear sRGB.
2. Conversion from linear sRGB to gamma-encoded sRGB.
The optional gamma argument specifies the exponent used when converting from linear sRGB to gamma-encoded RGB values. If not specified, a default gamma value is used for consistency with colorSRGBToOKLAB.
For more information about the OKLab color space and its relationship to sRGB, see <https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/color_value/oklab> .
**Syntax**
```
colorOKLABToSRGB(tuple [, gamma])
```
**Arguments**
- `tuple` β A tuple of three numeric values `L`, `a`, `b`, where `L` is in the range `[0...1]`. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. The exponent that is used to transform linear sRGB back to sRGB by applying `(x ^ (1 / gamma)) * 255` for each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (R, G, B) representing sRGB color values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert OKLAB to sRGB (Float)**
Query
```
SELECT colorOKLABToSRGB((0.4466, 0.0991, 0.44)) AS rgb;
```
Response
```
ββrgbβββββββββββββββββββββββ
β (198.07056923258935,0,0) β
ββββββββββββββββββββββββββββ
```
**Convert OKLAB to sRGB (UInt8)**
Query
```
WITH colorOKLABToSRGB((0.7, 0.1, 0.54)) AS t
SELECT tuple(toUInt8(t.1), toUInt8(t.2), toUInt8(t.3)) AS RGB;
```
Response
```
ββRGBβββββββββββ
β (255,0,0) β
ββββββββββββββββ
```
## colorOKLCHToSRGB[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorOKLCHToSRGB "Direct link to colorOKLCHToSRGB")
Introduced in: v25.7.0
Converts a colour from the **OKLCH** perceptual colour space to the familiar **sRGB** colour space.
If `L` is outside the range `[0...1]`, `C` is negative, or `H` is outside the range `[0...360]`, the result is implementation-defined.
Note
**OKLCH** is a cylindrical version of the OKLab colour space. It's three coordinates are `L` (the lightness in the range `[0...1]`), `C` (chroma `>= 0`) and `H` (hue in degrees from `[0...360]`). OKLab/OKLCH is designed to be perceptually uniform while remaining cheap to compute.
The conversion is the inverse of [`colorSRGBToOKLCH`](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLCH):
1. OKLCH to OKLab.
2. OKLab to Linear sRGB
3. Linear sRGB to sRGB
The second argument gamma is used at the last stage.
For references of colors in OKLCH space, and how they correspond to sRGB colors please see <https://oklch.com/>.
**Syntax**
```
colorOKLCHToSRGB(tuple [, gamma])
```
**Arguments**
- `tuple` β A tuple of three numeric values `L`, `C`, `H`, where `L` is in the range `[0...1]`, `C >= 0` and `H` is in the range `[0...360]`. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. The exponent that is used to transform linear sRGB back to sRGB by applying `(x ^ (1 / gamma)) * 255` for each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (R, G, B) representing sRGB color values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert OKLCH to sRGB**
```
SELECT colorOKLCHToSRGB((0.6, 0.12, 40)) AS rgb;
```
```
ββrgbββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (186.02058688365264,100.68677189684993,71.67819977081575) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
**Convert OKLCH to sRGB (UInt8)**
```
WITH colorOKLCHToSRGB((0.6, 0.12, 40)) AS t
SELECT tuple(toUInt8(t.1), toUInt8(t.2), toUInt8(t.3)) AS RGB;
```
```
ββRGBβββββββββββ
β (186,100,71) β
ββββββββββββββββ
```
## colorSRGBToOKLAB[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLAB "Direct link to colorSRGBToOKLAB")
Introduced in: v26.2.0
Converts a colour encoded in the **sRGB** colour space to the perceptually uniform **OKLAB** colour space.
If any input channel is outside `[0...255]` or the gamma value is non-positive, the behaviour is implementation-defined.
Note
**OKLAB** is a perceptually uniform color space. Its three coordinates are `L` (the lightness in the range `[0...1]`), `a (Green-Red axis)` and `b (Blue-Yellow axis)`. OKLab is designed to be perceptually uniform while remaining cheap to compute.
The conversion consists of two stages:
1. sRGB to Linear sRGB
2. Linear sRGB to OKLab
**Syntax**
```
colorSRGBToOKLAB(tuple[, gamma])
```
**Arguments**
- `tuple` β Tuple of three values R, G, B in the range `[0...255]`. [`Tuple(UInt8, UInt8, UInt8)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. Exponent that is used to linearize sRGB by applying `(x / 255)^gamma` to each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (L, a, b) representing the OKLAB color space values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert sRGB to OKLAB**
```
SELECT colorSRGBToOKLAB((128, 64, 32), 2.2) AS lab;
```
```
ββlabβββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (0.4436238384931984,0.07266246769242975,0.07500108778529994) β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## colorSRGBToOKLCH[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLCH "Direct link to colorSRGBToOKLCH")
Introduced in: v25.7.0
Converts a colour encoded in the **sRGB** colour space to the perceptually uniform **OKLCH** colour space.
If any input channel is outside `[0...255]` or the gamma value is non-positive, the behaviour is implementation-defined.
Note
**OKLCH** is a cylindrical version of the OKLab colour space. It's three coordinates are `L` (the lightness in the range `[0...1]`), `C` (chroma `>= 0`) and `H` (the hue in degrees from `[0...360]`). OKLab/OKLCH is designed to be perceptually uniform while remaining cheap to compute.
The conversion consists of three stages:
1. sRGB to Linear sRGB
2. Linear sRGB to OKLab
3. OKLab to OKLCH.
For references of colors in the OKLCH space, and how they correspond to sRGB colors, please see <https://OKLCH.com/>.
**Syntax**
```
colorSRGBToOKLCH(tuple[, gamma])
```
**Arguments**
- `tuple` β Tuple of three values R, G, B in the range `[0...255]`. [`Tuple(UInt8, UInt8, UInt8)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. Exponent that is used to linearize sRGB by applying `(x / 255)^gamma` to each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (L, C, H) representing the OKLCH color space values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert sRGB to OKLCH**
```
SELECT colorSRGBToOKLCH((128, 64, 32), 2.2) AS lch;
```
```
ββlchββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (0.4436238384931984,0.1044269954567863,45.90734548193018) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## connectionId[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#connectionId "Direct link to connectionId")
Introduced in: v21.3.0
Returns the connection ID of the client that submitted the current query. This function is most useful in debugging scenarios. It was created for compatibility with MySQL's `CONNECTION_ID` function. It is not typically used in production queries.
**Syntax**
```
connectionId()
```
**Arguments**
- None.
**Returned value**
Returns the connection ID of the current client. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT connectionId();
```
```
ββconnectionId()ββ
β 0 β
ββββββββββββββββββ
```
## countDigits[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#countDigits "Direct link to countDigits")
Introduced in: v20.8.0
Returns the number of decimal digits needed to represent a value.
Note
This function takes into account the scales of decimal values i.e., it calculates the result over the underlying integer type which is `(value * scale)`.
For example:
- `countDigits(42) = 2`
- `countDigits(42.000) = 5`
- `countDigits(0.04200) = 4`
Tip
You can check decimal overflow for `Decimal64` with `countDigits(x) > 18`, although it is slower than [`isDecimalOverflow`](https://clickhouse.com/docs/sql-reference/functions/other-functions#isDecimalOverflow).
**Syntax**
```
countDigits(x)
```
**Arguments**
- `x` β An integer or decimal value. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns the number of digits needed to represent `x`. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT countDigits(toDecimal32(1, 9)), countDigits(toDecimal32(-1, 9)),
countDigits(toDecimal64(1, 18)), countDigits(toDecimal64(-1, 18)),
countDigits(toDecimal128(1, 38)), countDigits(toDecimal128(-1, 38));
```
```
ββcountDigits(toDecimal32(1, 9))ββ¬βcountDigits(toDecimal32(-1, 9))ββ¬βcountDigits(toDecimal64(1, 18))ββ¬βcountDigits(toDecimal64(-1, 18))ββ¬βcountDigits(toDecimal128(1, 38))ββ¬βcountDigits(toDecimal128(-1, 38))ββ
β 10 β 10 β 19 β 19 β 39 β 39 β
ββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββ
```
## currentDatabase[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentDatabase "Direct link to currentDatabase")
Introduced in: v1.1.0
Returns the name of the current database. Useful in table engine parameters of `CREATE TABLE` queries where you need to specify the database.
Also see the [`SET` statement](https://clickhouse.com/docs/sql-reference/statements/use).
**Syntax**
```
currentDatabase()
```
**Aliases**: `current_database`, `SCHEMA`, `DATABASE`
**Arguments**
- None.
**Returned value**
Returns the current database name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT currentDatabase()
```
```
ββcurrentDatabase()ββ
β default β
βββββββββββββββββββββ
```
**SQL standard syntax without parentheses**
```
SELECT CURRENT_DATABASE
```
```
ββCURRENT_DATABASEββ
β default β
ββββββββββββββββββββ
```
## currentProfiles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentProfiles "Direct link to currentProfiles")
Introduced in: v21.9.0
Returns an array of the setting profiles for the current user.
**Syntax**
```
currentProfiles()
```
**Arguments**
- None.
**Returned value**
Returns an array of setting profiles for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT currentProfiles();
```
```
ββcurrentProfiles()ββββββββββββββββββββββββββββββ
β ['default', 'readonly_user', 'web_analytics'] β
βββββββββββββββββββββββββββββββββββββββββββββββββ
```
## currentQueryID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentQueryID "Direct link to currentQueryID")
Introduced in: v25.2.0
Returns current Query id.
**Syntax**
```
currentQueryID()
```
**Aliases**: `current_query_id`
**Arguments**
- None.
**Returned value**
**Examples**
**Example**
```
SELECT currentQueryID();
```
```
ββcurrentQueryID()ββββββββββββββββββββββ
β 1280d0e8-1a08-4524-be6e-77975bb68e7d β
ββββββββββββββββββββββββββββββββββββββββ
```
## currentRoles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentRoles "Direct link to currentRoles")
Introduced in: v21.9.0
Returns an array of the roles which are assigned to the current user.
**Syntax**
```
currentRoles()
```
**Arguments**
- None.
**Returned value**
Returns an array of the roles which are assigned to the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT currentRoles();
```
```
ββcurrentRoles()ββββββββββββββββββββββββββββββββββ
β ['sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## currentSchemas[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentSchemas "Direct link to currentSchemas")
Introduced in: v23.7.0
Same as function [`currentDatabase`](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentDatabase) but
- accepts a boolean argument which is ignored
- returns the database name as an array with a single value.
Function `currentSchemas` only exists for compatibility with PostgreSQL. Please use `currentDatabase` instead.
Also see the [`SET` statement](https://clickhouse.com/docs/sql-reference/statements/use).
**Syntax**
```
currentSchemas(bool)
```
**Aliases**: `current_schemas`
**Arguments**
- `bool` β A boolean value, which is ignored. [`Bool`](https://clickhouse.com/docs/sql-reference/data-types/boolean)
**Returned value**
Returns a single-element array with the name of the current database. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT currentSchemas(true)
```
```
ββcurrentSchemas(true)ββ
β ['default'] β
ββββββββββββββββββββββββ
```
## currentUser[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentUser "Direct link to currentUser")
Introduced in: v20.1.0
Returns the name of the current user. In case of a distributed query, the name of the user who initiated the query is returned.
**Syntax**
```
currentUser()
```
**Aliases**: `current_user`, `user`
**Arguments**
- None.
**Returned value**
Returns the name of the current user, otherwise the login of the user who initiated the query. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT currentUser()
```
```
ββcurrentUser()ββ
β default β
βββββββββββββββββ
```
**SQL standard syntax without parentheses**
```
SELECT CURRENT_USER
```
```
ββCURRENT_USERββ
β default β
ββββββββββββββββ
```
## defaultProfiles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultProfiles "Direct link to defaultProfiles")
Introduced in: v21.9.0
Returns an array of default setting profile names for the current user.
**Syntax**
```
defaultProfiles()
```
**Arguments**
- None.
**Returned value**
Returns an array of default setting profile names for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT defaultProfiles();
```
```
ββdefaultProfiles()ββ
β ['default'] β
βββββββββββββββββββββ
```
## defaultRoles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultRoles "Direct link to defaultRoles")
Introduced in: v21.9.0
Returns an array of default roles for the current user.
**Syntax**
```
defaultRoles()
```
**Arguments**
- None.
**Returned value**
Returns an array of default roles for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT defaultRoles();
```
```
ββdefaultRoles()ββββββββββββββββββββββββββββββββββ
β ['sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## defaultValueOfArgumentType[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultValueOfArgumentType "Direct link to defaultValueOfArgumentType")
Introduced in: v1.1.0
Returns the default value for a given data type. Does not include default values for custom columns set by the user.
**Syntax**
```
defaultValueOfArgumentType(expression)
```
**Arguments**
- `expression` β Arbitrary type of value or an expression that results in a value of an arbitrary type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns `0` for numbers, an empty string for strings or `NULL` for Nullable types. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`NULL`](https://clickhouse.com/docs/sql-reference/syntax#null)
**Examples**
**Usage example**
```
SELECT defaultValueOfArgumentType(CAST(1 AS Int8));
```
```
ββdefaultValueOfArgumentType(CAST(1, 'Int8'))ββ
β 0 β
βββββββββββββββββββββββββββββββββββββββββββββββ
```
**Nullable example**
```
SELECT defaultValueOfArgumentType(CAST(1 AS Nullable(Int8)));
```
```
ββdefaultValueOfArgumentType(CAST(1, 'Nullable(Int8)'))ββ
β α΄Ία΅α΄Έα΄Έ β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## defaultValueOfTypeName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultValueOfTypeName "Direct link to defaultValueOfTypeName")
Introduced in: v1.1.0
Returns the default value for the given type name.
**Syntax**
```
defaultValueOfTypeName(type)
```
**Arguments**
- `type` β A string representing a type name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the default value for the given type name: `0` for numbers, an empty string for strings, or `NULL` for Nullable [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`NULL`](https://clickhouse.com/docs/sql-reference/syntax#null)
**Examples**
**Usage example**
```
SELECT defaultValueOfTypeName('Int8');
```
```
ββdefaultValueOfTypeName('Int8')ββ
β 0 β
ββββββββββββββββββββββββββββββββββ
```
**Nullable example**
```
SELECT defaultValueOfTypeName('Nullable(Int8)');
```
```
ββdefaultValueOfTypeName('Nullable(Int8)')ββ
β α΄Ία΅α΄Έα΄Έ β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## displayName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#displayName "Direct link to displayName")
Introduced in: v22.11.0
Returns the value of `display_name` from [config](https://clickhouse.com/docs/operations/configuration-files) or the server's Fully Qualified Domain Name (FQDN) if not set.
**Syntax**
```
displayName()
```
**Arguments**
- None.
**Returned value**
Returns the value of `display_name` from config or server FQDN if not set. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT displayName();
```
```
ββdisplayName()ββ
β production β
βββββββββββββββββ
```
## dumpColumnStructure[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#dumpColumnStructure "Direct link to dumpColumnStructure")
Introduced in: v1.1.0
Outputs a detailed description of the internal structure of a column and its data type.
**Syntax**
```
dumpColumnStructure(x)
```
**Arguments**
- `x` β Value for which to get the description of. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a description of the column structure used for representing the value. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT dumpColumnStructure(CAST('2018-01-01 01:02:03', 'DateTime'));
```
```
ββdumpColumnStructure(CAST('2018-01-01 01:02:03', 'DateTime'))ββ
β DateTime, Const(size = 1, UInt32(size = 1)) β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## enabledProfiles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#enabledProfiles "Direct link to enabledProfiles")
Introduced in: v21.9.0
Returns an array of setting profile names which are enabled for the current user.
**Syntax**
```
enabledProfiles()
```
**Arguments**
- None.
**Returned value**
Returns an array of setting profile names which are enabled for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT enabledProfiles();
```
```
ββenabledProfiles()ββββββββββββββββββββββββββββββββββββββββββββββββββ
β ['default', 'readonly_user', 'web_analytics', 'batch_processing'] β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## enabledRoles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#enabledRoles "Direct link to enabledRoles")
Introduced in: v21.9.0
Returns an array of the roles which are enabled for the current user.
**Syntax**
```
enabledRoles()
```
**Arguments**
- None.
**Returned value**
Returns an array of role names which are enabled for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT enabledRoles();
```
```
ββenabledRoles()ββββββββββββββββββββββββββββββββββββββββββββββββββ
β ['general_data', 'sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## errorCodeToName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#errorCodeToName "Direct link to errorCodeToName")
Introduced in: v20.12.0
Returns the textual name of a numeric ClickHouse error code. The mapping from numeric error codes to error names is available [here](https://github.com/ClickHouse/ClickHouse/blob/master/src/Common/ErrorCodes.cpp).
**Syntax**
```
errorCodeToName(error_code)
```
**Arguments**
- `error_code` β ClickHouse error code. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns the textual name of `error_code`. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT errorCodeToName(252);
```
```
ββerrorCodeToName(252)ββ
β TOO_MANY_PARTS β
ββββββββββββββββββββββββ
```
## file[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#file "Direct link to file")
Introduced in: v21.3.0
Reads a file as a string and loads the data into the specified column. The file content is not interpreted.
Also see the [`file`](https://clickhouse.com/docs/sql-reference/table-functions/file) table function.
**Syntax**
```
file(path[, default])
```
**Arguments**
- `path` β The path of the file relative to the `user_files_path`. Supports wildcards `*`, `**`, `?`, `{abc,def}` and `{N..M}` where `N`, `M` are numbers and `'abc', 'def'` are strings. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `default` β The value returned if the file does not exist or cannot be accessed. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`NULL`](https://clickhouse.com/docs/sql-reference/syntax#null)
**Returned value**
Returns the file content as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Insert files into a table**
```
INSERT INTO table SELECT file('a.txt'), file('b.txt');
```
```
```
## filesystemAvailable[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemAvailable "Direct link to filesystemAvailable")
Introduced in: v20.1.0
Returns the amount of free space in the filesystem hosting the database persistence. The returned value is always smaller than the total free space ([`filesystemUnreserved`](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemUnreserved)) because some space is reserved for the operating system.
**Syntax**
```
filesystemAvailable([disk_name])
```
**Arguments**
- `disk_name` β Optional. The disk name to find the amount of free space for. If omitted, uses the default disk. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring)
**Returned value**
Returns the amount of remaining space available in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT formatReadableSize(filesystemAvailable()) AS "Available space";
```
```
ββAvailable spaceββ
β 30.75 GiB β
βββββββββββββββββββ
```
## filesystemCapacity[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemCapacity "Direct link to filesystemCapacity")
Introduced in: v20.1.0
Returns the capacity of the filesystem in bytes. Needs the [path](https://clickhouse.com/docs/operations/server-configuration-parameters/settings#path) to the data directory to be configured.
**Syntax**
```
filesystemCapacity([disk_name])
```
**Arguments**
- `disk_name` β Optional. The disk name to get the capacity for. If omitted, uses the default disk. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring)
**Returned value**
Returns the capacity of the filesystem in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT formatReadableSize(filesystemCapacity()) AS "Capacity";
```
```
ββCapacityβββ
β 39.32 GiB β
βββββββββββββ
```
## filesystemUnreserved[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemUnreserved "Direct link to filesystemUnreserved")
Introduced in: v22.12.0
Returns the total amount of free space on the filesystem hosting the database persistence (previously `filesystemFree`). See also [`filesystemAvailable`](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemAvailable).
**Syntax**
```
filesystemUnreserved([disk_name])
```
**Arguments**
- `disk_name` β Optional. The disk name for which to find the total amount of free space. If omitted, uses the default disk. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring)
**Returned value**
Returns the amount of free space in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT formatReadableSize(filesystemUnreserved()) AS "Free space";
```
```
ββFree spaceββ
β 32.39 GiB β
ββββββββββββββ
```
## finalizeAggregation[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#finalizeAggregation "Direct link to finalizeAggregation")
Introduced in: v1.1.0
Given an aggregation state, this function returns the result of aggregation (or the finalized state when using a [\-State](https://clickhouse.com/docs/sql-reference/aggregate-functions/combinators#-state) combinator).
**Syntax**
```
finalizeAggregation(state)
```
**Arguments**
- `state` β State of aggregation. [`AggregateFunction`](https://clickhouse.com/docs/sql-reference/data-types/aggregatefunction)
**Returned value**
Returns the finalized result of aggregation. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(arrayReduce('maxState', [1, 2, 3]));
```
```
ββfinalizeAggregation(arrayReduce('maxState', [1, 2, 3]))ββ
β 3 β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
**Combined with initializeAggregation**
```
WITH initializeAggregation('sumState', number) AS one_row_sum_state
SELECT
number,
finalizeAggregation(one_row_sum_state) AS one_row_sum,
runningAccumulate(one_row_sum_state) AS cumulative_sum
FROM numbers(5);
```
```
ββnumberββ¬βone_row_sumββ¬βcumulative_sumββ
β 0 β 0 β 0 β
β 1 β 1 β 1 β
β 2 β 2 β 3 β
β 3 β 3 β 6 β
β 4 β 4 β 10 β
ββββββββββ΄ββββββββββββββ΄βββββββββββββββββ
```
## flipCoordinates[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#flipCoordinates "Direct link to flipCoordinates")
Introduced in: v25.10.0
Flips the x and y coordinates of geometric objects. This operation swaps latitude and longitude, which is useful for converting between different coordinate systems or correcting coordinate order.
For a Point, it swaps the x and y coordinates. For complex geometries (LineString, Polygon, MultiPolygon, Ring, MultiLineString), it recursively applies the transformation to each coordinate pair.
The function supports both individual geometry types (Point, Ring, Polygon, MultiPolygon, LineString, MultiLineString) and the Geometry variant type.
**Syntax**
```
flipCoordinates(geometry)
```
**Arguments**
- `geometry` β The geometry to transform. Supported types: Point (Tuple(Float64, Float64)), Ring (Array(Point)), Polygon (Array(Ring)), MultiPolygon (Array(Polygon)), LineString (Array(Point)), MultiLineString (Array(LineString)), or Geometry (a variant containing any of these types).
**Returned value**
The geometry with flipped coordinates. The return type matches the input type. [`Point`](https://clickhouse.com/docs/sql-reference/data-types/geo#point) or [`Ring`](https://clickhouse.com/docs/sql-reference/data-types/geo#ring) or [`Polygon`](https://clickhouse.com/docs/sql-reference/data-types/geo#polygon) or [`MultiPolygon`](https://clickhouse.com/docs/sql-reference/data-types/geo#multipolygon) or [`LineString`](https://clickhouse.com/docs/sql-reference/data-types/geo#linestring) or [`MultiLineString`](https://clickhouse.com/docs/sql-reference/data-types/geo#multilinestring) or [`Geometry`](https://clickhouse.com/docs/sql-reference/data-types/geo)
**Examples**
**basic\_point**
```
SELECT flipCoordinates((1.0, 2.0));
```
```
(2.0, 1.0)
```
**ring**
```
SELECT flipCoordinates([(1.0, 2.0), (3.0, 4.0)]);
```
```
[(2.0, 1.0), (4.0, 3.0)]
```
**polygon**
```
SELECT flipCoordinates([[(1.0, 2.0), (3.0, 4.0)], [(5.0, 6.0), (7.0, 8.0)]]);
```
```
[[(2.0, 1.0), (4.0, 3.0)], [(6.0, 5.0), (8.0, 7.0)]]
```
**geometry\_wkt**
```
SELECT flipCoordinates(readWkt('POINT(10 20)'));
```
```
(20, 10)
```
**geometry\_polygon\_wkt**
```
SELECT flipCoordinates(readWkt('POLYGON((0 0, 5 0, 5 5, 0 5, 0 0))'));
```
```
[[(0, 0), (0, 5), (5, 5), (5, 0), (0, 0)]]
```
## formatQuery[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuery "Direct link to formatQuery")
Introduced in: v23.10.0
Returns a formatted, possibly multi-line, version of the given SQL query. Throws in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQuery(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuery('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT
a,
b
FROM tab
WHERE (a > 3) AND (b < 3)
```
## formatQueryOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQueryOrNull "Direct link to formatQueryOrNull")
Introduced in: v23.11.0
Returns a formatted, possibly multi-line, version of the given SQL query. Returns NULL in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQueryOrNull(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuery('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT
a,
b
FROM tab
WHERE (a > 3) AND (b < 3)
```
## formatQuerySingleLine[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuerySingleLine "Direct link to formatQuerySingleLine")
Introduced in: v23.10.0
Like formatQuery() but the returned formatted string contains no line breaks. Throws in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQuerySingleLine(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuerySingleLine('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT a, b FROM tab WHERE (a > 3) AND (b < 3)
```
## formatQuerySingleLineOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuerySingleLineOrNull "Direct link to formatQuerySingleLineOrNull")
Introduced in: v23.11.0
Like formatQuery() but the returned formatted string contains no line breaks. Returns NULL in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQuerySingleLineOrNull(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuerySingleLine('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT a, b FROM tab WHERE (a > 3) AND (b < 3)
```
## formatReadableDecimalSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize "Direct link to formatReadableDecimalSize")
Introduced in: v22.11.0
Given a size (number of bytes), this function returns a readable, rounded size with suffix (KB, MB, etc.) as a string.
The opposite operations of this function are [`parseReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize).
**Syntax**
```
formatReadableDecimalSize(x)
```
**Arguments**
- `x` β Size in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a readable, rounded size with suffix as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Format file sizes**
```
SELECT
arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
formatReadableDecimalSize(filesize_bytes) AS filesize
```
```
ββfilesize_bytesββ¬βfilesizeββββ
β 1 β 1.00 B β
β 1024 β 1.02 KB β
β 1048576 β 1.05 MB β
β 192851925 β 192.85 MB β
ββββββββββββββββββ΄βββββββββββββ
```
## formatReadableQuantity[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableQuantity "Direct link to formatReadableQuantity")
Introduced in: v20.10.0
Given a number, this function returns a rounded number with suffix (thousand, million, billion, etc.) as a string.
This function accepts any numeric type as input, but internally it casts them to `Float64`. Results might be suboptimal with large values.
**Syntax**
```
formatReadableQuantity(x)
```
**Arguments**
- `x` β A number to format. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a rounded number with suffix as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Format numbers with suffixes**
```
SELECT
arrayJoin([1024, 1234 * 1000, (4567 * 1000) * 1000, 98765432101234]) AS number,
formatReadableQuantity(number) AS number_for_humans
```
```
ββββββββββnumberββ¬βnumber_for_humansββ
β 1024 β 1.02 thousand β
β 1234000 β 1.23 million β
β 4567000000 β 4.57 billion β
β 98765432101234 β 98.77 trillion β
ββββββββββββββββββ΄ββββββββββββββββββββ
```
## formatReadableSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize "Direct link to formatReadableSize")
Introduced in: v1.1.0
Given a size (number of bytes), this function returns a readable, rounded size with suffix (KiB, MiB, etc.) as string.
The opposite operations of this function are [`parseReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize), [`parseReadableSizeOrZero`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrZero), and [`parseReadableSizeOrNull`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrNull). This function accepts any numeric type as input, but internally it casts them to `Float64`. Results might be suboptimal with large values.
**Syntax**
```
formatReadableSize(x)
```
**Aliases**: `FORMAT_BYTES`
**Arguments**
- `x` β Size in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a readable, rounded size with suffix as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Format file sizes**
```
SELECT
arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
formatReadableSize(filesize_bytes) AS filesize
```
```
ββfilesize_bytesββ¬βfilesizeββββ
β 1 β 1.00 B β
β 1024 β 1.00 KiB β
β 1048576 β 1.00 MiB β
β 192851925 β 183.92 MiB β
ββββββββββββββββββ΄βββββββββββββ
```
## formatReadableTimeDelta[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableTimeDelta "Direct link to formatReadableTimeDelta")
Introduced in: v20.12.0
Given a time interval (delta) in seconds, this function returns a time delta with year/month/day/hour/minute/second/millisecond/microsecond/nanosecond as a string.
This function accepts any numeric type as input, but internally it casts them to `Float64`. Results might be suboptimal with large values.
**Syntax**
```
formatReadableTimeDelta(column[, maximum_unit, minimum_unit])
```
**Arguments**
- `column` β A column with a numeric time delta. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `maximum_unit` β Optional. Maximum unit to show. Acceptable values: `nanoseconds`, `microseconds`, `milliseconds`, `seconds`, `minutes`, `hours`, `days`, `months`, `years`. Default value: `years`. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `minimum_unit` β Optional. Minimum unit to show. All smaller units are truncated. Acceptable values: `nanoseconds`, `microseconds`, `milliseconds`, `seconds`, `minutes`, `hours`, `days`, `months`, `years`. If explicitly specified value is bigger than `maximum_unit`, an exception will be thrown. Default value: `seconds` if `maximum_unit` is `seconds` or bigger, `nanoseconds` otherwise. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a time delta as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT
arrayJoin([100, 12345, 432546534]) AS elapsed,
formatReadableTimeDelta(elapsed) AS time_delta
```
```
βββββelapsedββ¬βtime_deltaββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β 100 β 1 minute and 40 seconds β
β 12345 β 3 hours, 25 minutes and 45 seconds β
β 432546534 β 13 years, 8 months, 17 days, 7 hours, 48 minutes and 54 secondsβ
ββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
**With maximum unit**
```
SELECT
arrayJoin([100, 12345, 432546534]) AS elapsed,
formatReadableTimeDelta(elapsed, 'minutes') AS time_delta
```
```
βββββelapsedββ¬βtime_deltaββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β 100 β 1 minute and 40 seconds β
β 12345 β 205 minutes and 45 seconds β
β 432546534 β 7209108 minutes and 54 seconds β
ββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## fuzzQuery[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#fuzzQuery "Direct link to fuzzQuery")
Introduced in: v26.2.0
Parses the given query string and applies random AST mutations (fuzzing) to it. Returns the fuzzed query as a string. Non-deterministic: each call may produce a different result. Requires `allow_fuzz_query_functions = 1`.
**Syntax**
```
fuzzQuery(query)
```
**Arguments**
- `query` β The SQL query to be fuzzed. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The fuzzed query string [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**basic**
```
SET allow_fuzz_query_functions = 1; SELECT fuzzQuery('SELECT 1');
```
```
```
## generateRandomStructure[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#generateRandomStructure "Direct link to generateRandomStructure")
Introduced in: v23.5.0
Generates random table structure in the format `column1_name column1_type, column2_name column2_type, ...`.
**Syntax**
```
generateRandomStructure([number_of_columns, seed])
```
**Arguments**
- `number_of_columns` β The desired number of columns in the resultant table structure. If set to 0 or `Null`, the number of columns will be random from 1 to 128. Default value: `Null`. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
- `seed` β Random seed to produce stable results. If seed is not specified or set to `Null`, it is randomly generated. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Randomly generated table structure. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT generateRandomStructure()
```
```
c1 Decimal32(5), c2 Date, c3 Tuple(LowCardinality(String), Int128, UInt64, UInt16, UInt8, IPv6), c4 Array(UInt128), c5 UInt32, c6 IPv4, c7 Decimal256(64), c8 Decimal128(3), c9 UInt256, c10 UInt64, c11 DateTime
```
**with specified number of columns**
```
SELECT generateRandomStructure(1)
```
```
c1 Map(UInt256, UInt16)
```
**with specified seed**
```
SELECT generateRandomStructure(NULL, 33)
```
```
c1 DateTime, c2 Enum8('c2V0' = 0, 'c2V1' = 1, 'c2V2' = 2, 'c2V3' = 3), c3 LowCardinality(Nullable(FixedString(30))), c4 Int16, c5 Enum8('c5V0' = 0, 'c5V1' = 1, 'c5V2' = 2, 'c5V3' = 3), c6 Nullable(UInt8), c7 String, c8 Nested(e1 IPv4, e2 UInt8, e3 UInt16, e4 UInt16, e5 Int32, e6 Map(Date, Decimal256(70)))
```
## generateSerialID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#generateSerialID "Direct link to generateSerialID")
Introduced in: v25.1.0
Generates and returns sequential numbers starting from the previous counter value. This function takes a string argument - a series identifier, and an optional starting value. The server should be configured with Keeper. The series are stored in Keeper nodes under the path, which can be configured in [`series_keeper_path`](https://clickhouse.com/docs/operations/server-configuration-parameters/settings#series_keeper_path) in the server configuration.
**Syntax**
```
generateSerialID(series_identifier[, start_value])
```
**Arguments**
- `series_identifier` β Series identifier [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `start_value` β Optional. Starting value for the counter. Defaults to 0. Note: this value is only used when creating a new series and is ignored if the series already exists [`UInt*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns sequential numbers starting from the previous counter value. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**first call**
```
SELECT generateSerialID('id1')
```
```
ββgenerateSerialID('id1')βββ
β 1 β
ββββββββββββββββββββββββββββ
```
**second call**
```
SELECT generateSerialID('id1')
```
```
ββgenerateSerialID('id1')βββ
β 2 β
ββββββββββββββββββββββββββββ
```
**column call**
```
SELECT *, generateSerialID('id1') FROM test_table
```
```
ββCounterIDββ¬βUserIDββ¬βverββ¬βgenerateSerialID('id1')βββ
β 1 β 3 β 3 β 3 β
β 1 β 1 β 1 β 4 β
β 1 β 2 β 2 β 5 β
β 1 β 5 β 5 β 6 β
β 1 β 4 β 4 β 7 β
βββββββββββββ΄βββββββββ΄ββββββ΄βββββββββββββββββββββββββββ
```
**with start value**
```
SELECT generateSerialID('id2', 100)
```
```
ββgenerateSerialID('id2', 100)βββ
β 100 β
βββββββββββββββββββββββββββββββββ
```
**with start value second call**
```
SELECT generateSerialID('id2', 100)
```
```
ββgenerateSerialID('id2', 100)βββ
β 101 β
βββββββββββββββββββββββββββββββββ
```
## getClientHTTPHeader[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getClientHTTPHeader "Direct link to getClientHTTPHeader")
Introduced in: v24.5.0
Gets the value of an HTTP header. If there is no such header or the current request is not performed via the HTTP interface, the function returns an empty string. Certain HTTP headers (e.g., `Authentication` and `X-ClickHouse-*`) are restricted.
Note
Setting `allow_get_client_http_header` is required
The function requires the setting `allow_get_client_http_header` to be enabled. The setting is not enabled by default for security reasons, because some headers, such as `Cookie`, could contain sensitive info.
HTTP headers are case sensitive for this function. If the function is used in the context of a distributed query, it returns non-empty result only on the initiator node.
**Syntax**
```
getClientHTTPHeader(name)
```
**Arguments**
- `name` β The HTTP header name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the value of the header. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT getClientHTTPHeader('Content-Type');
```
```
ββgetClientHTTPHeader('Content-Type')ββ
β application/x-www-form-urlencoded β
βββββββββββββββββββββββββββββββββββββββ
```
## getMacro[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMacro "Direct link to getMacro")
Introduced in: v20.1.0
Returns the value of a macro from the server configuration file. Macros are defined in the [`<macros>`](https://clickhouse.com/docs/operations/server-configuration-parameters/settings#macros) section of the configuration file and can be used to distinguish servers by convenient names even if they have complicated hostnames. If the function is executed in the context of a distributed table, it generates a normal column with values relevant to each shard.
**Syntax**
```
getMacro(name)
```
**Arguments**
- `name` β The name of the macro to retrieve. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the value of the specified macro. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Basic usage**
```
SELECT getMacro('test');
```
```
ββgetMacro('test')ββ
β Value β
ββββββββββββββββββββ
```
## getMaxTableNameLengthForDatabase[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMaxTableNameLengthForDatabase "Direct link to getMaxTableNameLengthForDatabase")
Introduced in: v25.1.0
Returns the maximum table name length in a specified database.
**Syntax**
```
getMaxTableNameLengthForDatabase(database_name)
```
**Arguments**
- `database_name` β The name of the specified database. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the length of the maximum table name, an Integer
**Examples**
**typical**
```
SELECT getMaxTableNameLengthForDatabase('default');
```
```
ββgetMaxTableNameLengthForDatabase('default')ββ
β 206 β
βββββββββββββββββββββββββββββββββββββββββββββββ
```
## getMergeTreeSetting[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMergeTreeSetting "Direct link to getMergeTreeSetting")
Introduced in: v25.6.0
Returns the current value of a MergeTree setting.
**Syntax**
```
getMergeTreeSetting(setting_name)
```
**Arguments**
- `setting_name` β The setting name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the merge tree setting's current value.
**Examples**
**Usage example**
```
SELECT getMergeTreeSetting('index_granularity');
```
```
ββgetMergeTreeSetting('index_granularity')ββ
β 8192 β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## getOSKernelVersion[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getOSKernelVersion "Direct link to getOSKernelVersion")
Introduced in: v21.11.0
Returns a string with the OS kernel version.
**Syntax**
```
getOSKernelVersion()
```
**Arguments**
- None.
**Returned value**
Returns the current OS kernel version. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT getOSKernelVersion();
```
```
ββgetOSKernelVersion()βββββ
β Linux 4.15.0-55-generic β
βββββββββββββββββββββββββββ
```
## getServerPort[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getServerPort "Direct link to getServerPort")
Introduced in: v21.10.0
Returns the server's port number for a given protocol.
**Syntax**
```
getServerPort(port_name)
```
**Arguments**
- `port_name` β The name of the port. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the server port number. [`UInt16`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT getServerPort('tcp_port');
```
```
ββgetServerPort('tcp_port')ββ
β 9000 β
βββββββββββββββββββββββββββββ
```
## getServerSetting[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getServerSetting "Direct link to getServerSetting")
Introduced in: v25.6.0
Returns the currently set value, given a server setting name.
**Syntax**
```
getServerSetting(setting_name')
```
**Arguments**
- `setting_name` β The server setting name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the server setting's current value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT getServerSetting('allow_use_jemalloc_memory');
```
```
ββgetServerSetting('allow_use_jemalloc_memory')ββ
β true β
βββββββββββββββββββββββββββββββββββββββββββββββββ
```
## getSetting[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSetting "Direct link to getSetting")
Introduced in: v20.7.0
Returns the current value of a setting.
**Syntax**
```
getSetting(setting_name)
```
**Arguments**
- `setting_Name` β The setting name. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the setting's current value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT getSetting('enable_analyzer');
SET enable_analyzer = false;
SELECT getSetting('enable_analyzer');
```
```
ββgetSetting('β―_analyzer')ββ
β true β
ββββββββββββββββββββββββββββ
ββgetSetting('β―_analyzer')ββ
β false β
ββββββββββββββββββββββββββββ
```
## getSettingOrDefault[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSettingOrDefault "Direct link to getSettingOrDefault")
Introduced in: v24.10.0
Returns the current value of a setting or returns the default value specified in the second argument if the setting is not set in the current profile.
**Syntax**
```
getSettingOrDefault(setting_name, default_value)
```
**Arguments**
- `setting_name` β The setting name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `default_value` β Value to return if custom\_setting is not set. Value may be of any data type or Null.
**Returned value**
Returns the current value of the specified setting or `default_value` if the setting is not set.
**Examples**
**Usage example**
```
SELECT getSettingOrDefault('custom_undef1', 'my_value');
SELECT getSettingOrDefault('custom_undef2', 100);
SELECT getSettingOrDefault('custom_undef3', NULL);
```
```
my_value
100
NULL
```
## getSizeOfEnumType[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSizeOfEnumType "Direct link to getSizeOfEnumType")
Introduced in: v1.1.0
Returns the number of fields in the given [`Enum`](https://clickhouse.com/docs/sql-reference/data-types/enum).
**Syntax**
```
getSizeOfEnumType(x)
```
**Arguments**
- `x` β Value of type `Enum`. [`Enum`](https://clickhouse.com/docs/sql-reference/data-types/enum)
**Returned value**
Returns the number of fields with `Enum` input values. [`UInt8/16`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT getSizeOfEnumType(CAST('a' AS Enum8('a' = 1, 'b' = 2))) AS x;
```
```
ββxββ
β 2 β
βββββ
```
## getSubcolumn[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSubcolumn "Direct link to getSubcolumn")
Introduced in: v23.3.0
Receives the expression or identifier and constant string with the name of subcolumn.
Returns requested subcolumn extracted from the expression.
**Syntax**
```
getSubcolumn(nested_value, subcolumn_name)
```
**Arguments**
- None.
**Returned value**
**Examples**
**getSubcolumn**
```
SELECT getSubcolumn(array_col, 'size0'), getSubcolumn(tuple_col, 'elem_name')
```
```
```
## getTypeSerializationStreams[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getTypeSerializationStreams "Direct link to getTypeSerializationStreams")
Introduced in: v22.6.0
Enumerates stream paths of a data type. This function is intended for developmental use.
**Syntax**
```
getTypeSerializationStreams(col)
```
**Arguments**
- `col` β Column or string representation of a data-type from which the data type will be detected. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns an array with all the serialization sub-stream paths. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**tuple**
```
SELECT getTypeSerializationStreams(tuple('a', 1, 'b', 2))
```
```
['{TupleElement(1), Regular}','{TupleElement(2), Regular}','{TupleElement(3), Regular}','{TupleElement(4), Regular}']
```
**map**
```
SELECT getTypeSerializationStreams('Map(String, Int64)')
```
```
['{ArraySizes}','{ArrayElements, TupleElement(keys), Regular}','{ArrayElements, TupleElement(values), Regular}']
```
## globalVariable[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#globalVariable "Direct link to globalVariable")
Introduced in: v20.5.0
Takes a constant string argument and returns the value of the global variable with that name. This function is intended for compatibility with MySQL and not needed or useful for normal operation of ClickHouse. Only few dummy global variables are defined.
**Syntax**
```
globalVariable(name)
```
**Arguments**
- `name` β Global variable name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the value of variable `name`. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**globalVariable**
```
SELECT globalVariable('max_allowed_packet')
```
```
67108864
```
## hasColumnInTable[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#hasColumnInTable "Direct link to hasColumnInTable")
Introduced in: v1.1.0
Checks if a specific column exists in a database table. For elements in a nested data structure, the function checks for the existence of a column. For the nested data structure itself, the function returns `0`.
**Syntax**
```
hasColumnInTable([hostname[, username[, password]],]database, table, column)
```
**Arguments**
- `database` β Name of the database. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `table` β Name of the table. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `column` β Name of the column. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `hostname` β Optional. Remote server name to perform the check on. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `username` β Optional. Username for remote server. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `password` β Optional. Password for remote server. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns `1` if the given column exists, `0` otherwise. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Check an existing column**
```
SELECT hasColumnInTable('system','metrics','metric')
```
```
1
```
**Check a non-existing column**
```
SELECT hasColumnInTable('system','metrics','non-existing_column')
```
```
0
```
## hasThreadFuzzer[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#hasThreadFuzzer "Direct link to hasThreadFuzzer")
Introduced in: v20.6.0
Returns whether the thread fuzzer is enabled. THis function is only useful for testing and debugging.
**Syntax**
```
hasThreadFuzzer()
```
**Arguments**
- None.
**Returned value**
Returns whether Thread Fuzzer is effective. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Check Thread Fuzzer status**
```
SELECT hasThreadFuzzer()
```
```
ββhasThreadFuzzer()ββ
β 0 β
βββββββββββββββββββββ
```
## hostName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#hostName "Direct link to hostName")
Introduced in: v20.5.0
Returns the name of the host on which this function was executed. If the function executes on a remote server (distributed processing), the remote server name is returned. If the function executes in the context of a distributed table, it generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
hostName()
```
**Aliases**: `hostname`
**Arguments**
- None.
**Returned value**
Returns the host name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT hostName()
```
```
ββhostName()ββ
β clickhouse β
ββββββββββββββ
```
## icebergBucket[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#icebergBucket "Direct link to icebergBucket")
Introduced in: v25.5.0
Implements logic for the [iceberg bucket transform](https://iceberg.apache.org/spec/#bucket-transform-details.)
**Syntax**
```
icebergBucket(N, value)
```
**Arguments**
- `N` β The number of buckets, modulo. [`const (U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
- `value` β The source value to transform. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Bool`](https://clickhouse.com/docs/sql-reference/data-types/boolean) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring) or [`UUID`](https://clickhouse.com/docs/sql-reference/data-types/uuid) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`Time`](https://clickhouse.com/docs/sql-reference/data-types/time) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
**Returned value**
Returns a 32-bit hash of the source value. [`Int32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Example**
```
SELECT icebergBucket(5, 1.0 :: Float32)
```
```
4
```
## icebergTruncate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#icebergTruncate "Direct link to icebergTruncate")
Introduced in: v25.3.0
Implements logic of iceberg truncate transform: <https://iceberg.apache.org/spec/#truncate-transform-details>.
**Syntax**
```
icebergTruncate(N, value)
```
**Arguments**
- `value` β The value to transform. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
The same type as the argument
**Examples**
**Example**
```
SELECT icebergTruncate(3, 'iceberg')
```
```
ice
```
## identity[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#identity "Direct link to identity")
Introduced in: v1.1.0
This function returns the argument you pass to it, which is useful for debugging and testing. It lets you bypass index usage to see full scan performance instead. The query analyzer ignores anything inside identity functions when looking for indexes to use, and it also disables constant folding.
**Syntax**
```
identity(x)
```
**Arguments**
- `x` β Input value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the input value unchanged. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT identity(42)
```
```
42
```
## ignore[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#ignore "Direct link to ignore")
Introduced in: v1.1.0
Accepts arbitrary arguments and unconditionally returns `0`.
**Syntax**
```
ignore(x)
```
**Arguments**
- `x` β An input value which is unused and passed only so as to avoid a syntax error. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Always returns `0`. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT ignore(0, 'ClickHouse', NULL)
```
```
ββignore(0, 'ClickHouse', NULL)ββ
β 0 β
βββββββββββββββββββββββββββββββββ
```
## indexHint[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#indexHint "Direct link to indexHint")
Introduced in: v1.1.0
This function is intended for debugging and introspection. It ignores its argument and always returns 1. The arguments are not evaluated.
During index analysis, the argument of this function is assumed to not be wrapped in `indexHint`. This allows you to select data in index ranges by the corresponding condition but without further filtering by this condition. The index in ClickHouse is sparse and using `indexHint` will yield more data than specifying the same condition directly.
Explanation
When you run:
```
SELECT * FROM test WHERE key = 123;
```
ClickHouse does two things:
1. Uses the index to find which granules (blocks of ~8192 rows) might contain `key = 123`
2. Reads those granules and filters them row-by-row to return only rows where `key = 123`
So even if it reads 8,192 rows from disk, it only returns the 1 row that actually matches.
With `indexHint`, when you run:
```
SELECT * FROM test WHERE indexHint(key = 123);
```
ClickHouse does only one thing:
1. Uses the index to find which granules might contain key = 123 and returns all rows from those granules **without** filtering.
It returns all 8,192 rows, including rows where `key = 456`, `key = 789`, etc. (Everything that happened to be stored in the same granule.) `indexHint()` is not for performance. It's for debugging and understanding how ClickHouse's index works:
- Which granules does my condition select?
- How many rows are in those granules?
- Is my index being used effectively?
Note: It is not possible to optimize a query with the `indexHint` function. The `indexHint` function does not optimize the query, as it does not provide any additional information for the query analysis. Having an expression inside the `indexHint` function is not anyhow better than without the `indexHint` function. The `indexHint` function can be used only for introspection and debugging purposes and it does not improve performance. If you see the usage of `indexHint` by anyone other than ClickHouse contributors, it is likely a mistake and you should remove it.
**Syntax**
```
indexHint(expression)
```
**Arguments**
- `expression` β Any expression for index range selection. [`Expression`](https://clickhouse.com/docs/sql-reference/data-types/special-data-types/expression)
**Returned value**
Returns `1` in all cases. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example with date filtering**
```
SELECT FlightDate AS k, count() FROM ontime WHERE indexHint(k = '2025-09-15') GROUP BY k ORDER BY k ASC;
```
```
βββββββββββkββ¬βcount()ββ
β 2025-09-14 β 7071 β
β 2025-09-15 β 16428 β
β 2025-09-16 β 1077 β
β 2025-09-30 β 8167 β
ββββββββββββββ΄ββββββββββ
```
## initialQueryID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryID "Direct link to initialQueryID")
Introduced in: v1.1.0
Returns the ID of the initial current query. Other parameters of a query can be extracted from field `initial_query_id` in [`system.query_log`](https://clickhouse.com/docs/operations/system-tables/query_log).
In contrast to [`queryID`](https://clickhouse.com/docs/sql-reference/functions/other-functions#queryID) function, `initialQueryID` returns the same results on different shards.
**Syntax**
```
initialQueryID()
```
**Aliases**: `initial_query_id`
**Arguments**
- None.
**Returned value**
Returns the ID of the initial current query. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT initialQueryID() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
```
```
ββcount(DISTINCT t)ββ
β 1 β
βββββββββββββββββββββ
```
## initialQueryStartTime[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryStartTime "Direct link to initialQueryStartTime")
Introduced in: v25.4.0
Returns the start time of the initial current query. `initialQueryStartTime` returns the same results on different shards.
**Syntax**
```
initialQueryStartTime()
```
**Aliases**: `initial_query_start_time`
**Arguments**
- None.
**Returned value**
Returns the start time of the initial current query. [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
**Examples**
**Usage example**
```
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT initialQueryStartTime() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
```
```
ββcount(DISTINCT t)ββ
β 1 β
βββββββββββββββββββββ
```
## initializeAggregation[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#initializeAggregation "Direct link to initializeAggregation")
Introduced in: v20.6.0
Calculates the result of an aggregate function based on a single value. This function can be used to initialize aggregate functions with combinator [\-State](https://clickhouse.com/docs/sql-reference/aggregate-functions/combinators#-state). You can create states of aggregate functions and insert them to columns of type [`AggregateFunction`](https://clickhouse.com/docs/sql-reference/data-types/aggregatefunction) or use initialized aggregates as default values.
**Syntax**
```
initializeAggregation(aggregate_function, arg1[, arg2, ...])
```
**Arguments**
- `aggregate_function` β Name of the aggregation function to initialize. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `arg1[, arg2, ...]` β Arguments of the aggregate function. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the result of aggregation for every row passed to the function. The return type is the same as the return type of the function that `initializeAggregation` takes as a first argument. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Basic usage with uniqState**
```
SELECT uniqMerge(state) FROM (SELECT initializeAggregation('uniqState', number % 3) AS state FROM numbers(10000));
```
```
ββuniqMerge(state)ββ
β 3 β
ββββββββββββββββββββ
```
**Usage with sumState and finalizeAggregation**
```
SELECT finalizeAggregation(state), toTypeName(state) FROM (SELECT initializeAggregation('sumState', number % 3) AS state FROM numbers(5));
```
```
ββfinalizeAggregation(state)ββ¬βtoTypeName(state)ββββββββββββββ
β 0 β AggregateFunction(sum, UInt8) β
β 1 β AggregateFunction(sum, UInt8) β
β 2 β AggregateFunction(sum, UInt8) β
β 0 β AggregateFunction(sum, UInt8) β
β 1 β AggregateFunction(sum, UInt8) β
ββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββ
```
## isConstant[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#isConstant "Direct link to isConstant")
Introduced in: v20.3.0
Returns whether the argument is a constant expression. A constant expression is an expression whose result is known during query analysis, i.e. before execution. For example, expressions over [literals](https://clickhouse.com/docs/sql-reference/syntax#literals) are constant expressions. This function is mostly intended for development, debugging and demonstration.
**Syntax**
```
isConstant(x)
```
**Arguments**
- `x` β An expression to check. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns `1` if `x` is constant, `0` if `x` is non-constant. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Constant expression**
```
SELECT isConstant(x + 1)
FROM (SELECT 43 AS x)
```
```
ββisConstant(plus(x, 1))ββ
β 1 β
ββββββββββββββββββββββββββ
```
**Constant with function**
```
WITH 3.14 AS pi
SELECT isConstant(cos(pi))
```
```
ββisConstant(cos(pi))ββ
β 1 β
βββββββββββββββββββββββ
```
**Non-constant expression**
```
SELECT isConstant(number)
FROM numbers(1)
```
```
ββisConstant(number)ββ
β 0 β
ββββββββββββββββββββββ
```
**Behavior of the now() function**
```
SELECT isConstant(now())
```
```
ββisConstant(now())ββ
β 1 β
βββββββββββββββββββββ
```
## isDecimalOverflow[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#isDecimalOverflow "Direct link to isDecimalOverflow")
Introduced in: v20.8.0
Checks if a decimal number has too many digits to fit properly in a Decimal data type with given precision.
**Syntax**
```
isDecimalOverflow(value[, precision])
```
**Arguments**
- `value` β Decimal value to check. [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `precision` β Optional. The precision of the Decimal type. If omitted, the initial precision of the first argument is used. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns `1` if the decimal value has more digits than allowed by its precision, `0` if the decimal value satisfies the specified precision. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT isDecimalOverflow(toDecimal32(1000000000, 0), 9),
isDecimalOverflow(toDecimal32(1000000000, 0)),
isDecimalOverflow(toDecimal32(-1000000000, 0), 9),
isDecimalOverflow(toDecimal32(-1000000000, 0));
```
```
ββisDecimalOverflow(toDecimal32(1000000000, 0), 9)ββ¬βisDecimalOverflow(toDecimal32(1000000000, 0))ββ¬βisDecimalOverflow(toDecimal32(-1000000000, 0), 9)ββ¬βisDecimalOverflow(toDecimal32(-1000000000, 0))ββ
β 1 β 1 β 1 β 1 β
ββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββ
```
## joinGet[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGet "Direct link to joinGet")
Introduced in: v18.16.0
Allows you to extract data from a table the same way as from a dictionary. Gets data from Join tables using the specified join key.
Note
Only supports tables created with the `ENGINE = Join(ANY, LEFT, <join_keys>)` [statement](https://clickhouse.com/docs/engines/table-engines/special/join).
**Syntax**
```
joinGet(join_storage_table_name, value_column, join_keys)
```
**Arguments**
- `join_storage_table_name` β An identifier which indicates where to perform the search. The identifier is searched in the default database (see parameter `default_database` in the config file). To override the default database, use the `USE database_name` query or specify the database and the table through a dot, like `database_name.table_name`. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `value_column` β The name of the column of the table that contains required data. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `join_keys` β A list of join keys. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns list of values corresponded to list of keys. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13);
SELECT joinGet(db_test.id_val, 'val', toUInt32(1));
```
```
ββjoinGet(db_test.id_val, 'val', toUInt32(1))ββ
β 11 β
βββββββββββββββββββββββββββββββββββββββββββββββ
```
**Usage with table from current database**
```
USE db_test;
SELECT joinGet(id_val, 'val', toUInt32(2));
```
```
ββjoinGet(id_val, 'val', toUInt32(2))ββ
β 12 β
βββββββββββββββββββββββββββββββββββββββ
```
**Using arrays as join keys**
```
CREATE TABLE some_table (id1 UInt32, id2 UInt32, name String) ENGINE = Join(ANY, LEFT, id1, id2);
INSERT INTO some_table VALUES (1, 11, 'a') (2, 12, 'b') (3, 13, 'c');
SELECT joinGet(some_table, 'name', 1, 11);
```
```
ββjoinGet(some_table, 'name', 1, 11)ββ
β a β
ββββββββββββββββββββββββββββββββββββββ
```
## joinGetOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGetOrNull "Direct link to joinGetOrNull")
Introduced in: v20.4.0
Allows you to extract data from a table the same way as from a dictionary. Gets data from Join tables using the specified join key. Unlike [`joinGet`](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGet) it returns `NULL` when the key is missing.
Note
Only supports tables created with the `ENGINE = Join(ANY, LEFT, <join_keys>)` [statement](https://clickhouse.com/docs/engines/table-engines/special/join).
**Syntax**
```
joinGetOrNull(join_storage_table_name, value_column, join_keys)
```
**Arguments**
- `join_storage_table_name` β An identifier which indicates where to perform the search. The identifier is searched in the default database (see parameter default\_database in the config file). To override the default database, use the `USE database_name` query or specify the database and the table through a dot, like `database_name.table_name`. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `value_column` β The name of the column of the table that contains required data. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `join_keys` β A list of join keys. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a list of values corresponding to the list of keys, or `NULL` if a key is not found. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13);
SELECT joinGetOrNull(db_test.id_val, 'val', toUInt32(1)), joinGetOrNull(db_test.id_val, 'val', toUInt32(999));
```
```
ββjoinGetOrNull(db_test.id_val, 'val', toUInt32(1))ββ¬βjoinGetOrNull(db_test.id_val, 'val', toUInt32(999))ββ
β 11 β α΄Ία΅α΄Έα΄Έ β
βββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## lowCardinalityIndices[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#lowCardinalityIndices "Direct link to lowCardinalityIndices")
Introduced in: v18.12.0
Returns the position of a value in the dictionary of a [LowCardinality](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality) column. Positions start at 1. Since LowCardinality have per-part dictionaries, this function may return different positions for the same value in different parts.
**Syntax**
```
lowCardinalityIndices(col)
```
**Arguments**
- `col` β A low cardinality column. [`LowCardinality`](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality)
**Returned value**
The position of the value in the dictionary of the current part. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage examples**
```
DROP TABLE IF EXISTS test;
CREATE TABLE test (s LowCardinality(String)) ENGINE = Memory;
-- create two parts:
INSERT INTO test VALUES ('ab'), ('cd'), ('ab'), ('ab'), ('df');
INSERT INTO test VALUES ('ef'), ('cd'), ('ab'), ('cd'), ('ef');
SELECT s, lowCardinalityIndices(s) FROM test;
```
```
ββsβββ¬βlowCardinalityIndices(s)ββ
β ab β 1 β
β cd β 2 β
β ab β 1 β
β ab β 1 β
β df β 3 β
ββββββ΄βββββββββββββββββββββββββββ
ββsβββ¬βlowCardinalityIndices(s)ββ
β ef β 1 β
β cd β 2 β
β ab β 3 β
β cd β 2 β
β ef β 1 β
ββββββ΄βββββββββββββββββββββββββββ
```
## lowCardinalityKeys[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#lowCardinalityKeys "Direct link to lowCardinalityKeys")
Introduced in: v18.12.0
Returns the dictionary values of a [LowCardinality](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality) column. If the block is smaller or larger than the dictionary size, the result will be truncated or extended with default values. Since LowCardinality have per-part dictionaries, this function may return different dictionary values in different parts.
**Syntax**
```
lowCardinalityKeys(col)
```
**Arguments**
- `col` β A low cardinality column. [`LowCardinality`](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality)
**Returned value**
Returns the dictionary keys. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**lowCardinalityKeys**
```
DROP TABLE IF EXISTS test;
CREATE TABLE test (s LowCardinality(String)) ENGINE = Memory;
-- create two parts:
INSERT INTO test VALUES ('ab'), ('cd'), ('ab'), ('ab'), ('df');
INSERT INTO test VALUES ('ef'), ('cd'), ('ab'), ('cd'), ('ef');
SELECT s, lowCardinalityKeys(s) FROM test;
```
```
ββsβββ¬βlowCardinalityKeys(s)ββ
β ef β β
β cd β ef β
β ab β cd β
β cd β ab β
β ef β β
ββββββ΄ββββββββββββββββββββββββ
ββsβββ¬βlowCardinalityKeys(s)ββ
β ab β β
β cd β ab β
β ab β cd β
β ab β df β
β df β β
ββββββ΄ββββββββββββββββββββββββ
```
## materialize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#materialize "Direct link to materialize")
Introduced in: v1.1.0
Turns a constant into a full column containing a single value. Full columns and constants are represented differently in memory. Functions usually execute different code for normal and constant arguments, although the result should typically be the same. This function can be used to debug this behavior.
**Syntax**
```
materialize(x)
```
**Arguments**
- `x` β A constant. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a full column containing the constant value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
-- In the example below the `countMatches` function expects a constant second argument.
-- This behaviour can be debugged by using the `materialize` function to turn a constant into a full column,
-- verifying that the function throws an error for a non-constant argument.
SELECT countMatches('foobarfoo', 'foo');
SELECT countMatches('foobarfoo', materialize('foo'));
```
```
2
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Illegal type of argument #2 'pattern' of function countMatches, expected constant String, got String
```
## minSampleSizeContinuous[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#minSampleSizeContinuous "Direct link to minSampleSizeContinuous")
Introduced in: v23.10.0
Calculates the minimum required sample size for an A/B test comparing means of a continuous metric in two samples.
Uses the formula described in [this article](https://towardsdatascience.com/required-sample-size-for-a-b-testing-6f6608dd330a). Assumes equal sizes of treatment and control groups. Returns the required sample size for one group (i.e. the sample size required for the whole experiment is twice the returned value). Also assumes equal variance of the test metric in treatment and control groups.
**Syntax**
```
minSampleSizeContinuous(baseline, sigma, mde, power, alpha)
```
**Aliases**: `minSampleSizeContinous`
**Arguments**
- `baseline` β Baseline value of a metric. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `sigma` β Baseline standard deviation of a metric. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `mde` β Minimum detectable effect (MDE) as percentage of the baseline value (e.g. for a baseline value 112.25 the MDE 0.03 means an expected change to 112.25 Β± 112.25\*0.03). [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `power` β Required statistical power of a test (1 - probability of Type II error). [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `alpha` β Required significance level of a test (probability of Type I error). [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a named Tuple with 3 elements: `minimum_sample_size`, `detect_range_lower` and `detect_range_upper`. These are respectively: the required sample size, the lower bound of the range of values not detectable with the returned required sample size, calculated as `baseline * (1 - mde)`, and the upper bound of the range of values not detectable with the returned required sample size, calculated as `baseline * (1 + mde)` (Float64). [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**minSampleSizeContinuous**
```
SELECT minSampleSizeContinuous(112.25, 21.1, 0.03, 0.80, 0.05) AS sample_size
```
```
(616.2931945826209,108.8825,115.6175)
```
## minSampleSizeConversion[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#minSampleSizeConversion "Direct link to minSampleSizeConversion")
Introduced in: v22.6.0
Calculates minimum required sample size for an A/B test comparing conversions (proportions) in two samples.
Uses the formula described in [this article](https://towardsdatascience.com/required-sample-size-for-a-b-testing-6f6608dd330a). Assumes equal sizes of treatment and control groups. Returns the sample size required for one group (i.e. the sample size required for the whole experiment is twice the returned value).
**Syntax**
```
minSampleSizeConversion(baseline, mde, power, alpha)
```
**Arguments**
- `baseline` β Baseline conversion. [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `mde` β Minimum detectable effect (MDE) as percentage points (e.g. for a baseline conversion 0.25 the MDE 0.03 means an expected change to 0.25 Β± 0.03). [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `power` β Required statistical power of a test (1 - probability of Type II error). [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `alpha` β Required significance level of a test (probability of Type I error). [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a named Tuple with 3 elements: `minimum_sample_size`, `detect_range_lower`, `detect_range_upper`. These are, respectively: the required sample size, the lower bound of the range of values not detectable with the returned required sample size, calculated as `baseline - mde`, the upper bound of the range of values not detectable with the returned required sample size, calculated as `baseline + mde`. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**minSampleSizeConversion**
```
SELECT minSampleSizeConversion(0.25, 0.03, 0.80, 0.05) AS sample_size
```
```
(3396.077603219163,0.22,0.28)
```
## neighbor[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#neighbor "Direct link to neighbor")
Introduced in: v20.1.0
Returns a value from a column at a specified offset from the current row. This function is deprecated and error-prone because it operates on the physical order of data blocks which may not correspond to the logical order expected by users. Consider using proper window functions instead.
The function can be enabled by setting `allow_deprecated_error_prone_window_functions = 1`.
**Syntax**
```
neighbor(column, offset[, default_value])
```
**Arguments**
- `column` β The source column. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
- `offset` β The offset from the current row. Positive values look forward, negative values look backward. [`Integer`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
- `default_value` β Optional. The value to return if the offset goes beyond the data bounds. If not specified, uses the default value for the column type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a value from the specified offset, or default if out of bounds. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT number, neighbor(number, 2) FROM system.numbers LIMIT 10;
```
```
ββnumberββ¬βneighbor(number, 2)ββ
β 0 β 2 β
β 1 β 3 β
β 2 β 4 β
β 3 β 5 β
β 4 β 6 β
β 5 β 7 β
β 6 β 8 β
β 7 β 9 β
β 8 β 0 β
β 9 β 0 β
ββββββββββ΄ββββββββββββββββββββββ
```
**With default value**
```
SELECT number, neighbor(number, 2, 999) FROM system.numbers LIMIT 10;
```
```
ββnumberββ¬βneighbor(number, 2, 999)ββ
β 0 β 2 β
β 1 β 3 β
β 2 β 4 β
β 3 β 5 β
β 4 β 6 β
β 5 β 7 β
β 6 β 8 β
β 7 β 9 β
β 8 β 999 β
β 9 β 999 β
ββββββββββ΄βββββββββββββββββββββββββββ
```
## normalizeQuery[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizeQuery "Direct link to normalizeQuery")
Introduced in: v20.8.0
Replaces literals, sequences of literals and complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with placeholder `?`.
**Syntax**
```
normalizeQuery(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the given sequence of characters with placeholders. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT normalizeQuery('[1, 2, 3, x]') AS query
```
```
ββqueryβββββ
β [?.., x] β
ββββββββββββ
```
## normalizeQueryKeepNames[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizeQueryKeepNames "Direct link to normalizeQueryKeepNames")
Introduced in: v21.2.0
Replaces literals and sequences of literals with placeholder `?` but does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs). This helps better analyze complex query logs.
**Syntax**
```
normalizeQueryKeepNames(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the given sequence of characters with placeholders. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT normalizeQuery('SELECT 1 AS aComplexName123'), normalizeQueryKeepNames('SELECT 1 AS aComplexName123')
```
```
ββnormalizeQuery('SELECT 1 AS aComplexName123')ββ¬βnormalizeQueryKeepNames('SELECT 1 AS aComplexName123')ββ
β SELECT ? AS `?` β SELECT ? AS aComplexName123 β
βββββββββββββββββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## normalizedQueryHash[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHash "Direct link to normalizedQueryHash")
Introduced in: v20.8.0
Returns identical 64 bit hash values without the values of literals for similar queries. Can be helpful in analyzing query logs.
**Syntax**
```
normalizedQueryHash(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a 64 bit hash value. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT normalizedQueryHash('SELECT 1 AS `xyz`') != normalizedQueryHash('SELECT 1 AS `abc`') AS res
```
```
ββresββ
β 1 β
βββββββ
```
## normalizedQueryHashKeepNames[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHashKeepNames "Direct link to normalizedQueryHashKeepNames")
Introduced in: v21.2.0
Like [`normalizedQueryHash`](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHash) it returns identical 64 bit hash values without the values of literals for similar queries, but it does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with a placeholder before hashing. Can be helpful in analyzing query logs.
**Syntax**
```
normalizedQueryHashKeepNames(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a 64 bit hash value. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT normalizedQueryHash('SELECT 1 AS `xyz123`') != normalizedQueryHash('SELECT 1 AS `abc123`') AS normalizedQueryHash;
SELECT normalizedQueryHashKeepNames('SELECT 1 AS `xyz123`') != normalizedQueryHashKeepNames('SELECT 1 AS `abc123`') AS normalizedQueryHashKeepNames;
```
```
ββnormalizedQueryHashββ
β 0 β
βββββββββββββββββββββββ
ββnormalizedQueryHashKeepNamesββ
β 1 β
ββββββββββββββββββββββββββββββββ
```
## parseReadableSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize "Direct link to parseReadableSize")
Introduced in: v24.6.0
Given a string containing a byte size and `B`, `KiB`, `KB`, `MiB`, `MB`, etc. as a unit (i.e. [ISO/IEC 80000-13](https://en.wikipedia.org/wiki/ISO/IEC_80000) or decimal byte unit), this function returns the corresponding number of bytes. If the function is unable to parse the input value, it throws an exception.
The inverse operations of this function are [`formatReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize) and [`formatReadableDecimalSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize).
**Syntax**
```
parseReadableSize(x)
```
**Arguments**
- `x` β Readable size with ISO/IEC 80000-13 or decimal byte unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the number of bytes, rounded up to the nearest integer. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB']) AS readable_sizes, parseReadableSize(readable_sizes) AS sizes;
```
```
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
ββββββββββββββββββ΄ββββββββββ
```
## parseReadableSizeOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrNull "Direct link to parseReadableSizeOrNull")
Introduced in: v24.6.0
Given a string containing a byte size and `B`, `KiB`, `KB`, `MiB`, `MB`, etc. as a unit (i.e. [ISO/IEC 80000-13](https://en.wikipedia.org/wiki/ISO/IEC_80000) or decimal byte unit), this function returns the corresponding number of bytes. If the function is unable to parse the input value, it returns `NULL`.
The inverse operations of this function are [`formatReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize) and [`formatReadableDecimalSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize).
**Syntax**
```
parseReadableSizeOrNull(x)
```
**Arguments**
- `x` β Readable size with ISO/IEC 80000-13 or decimal byte unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the number of bytes, rounded up to the nearest integer, or `NULL` if unable to parse the input [`Nullable(UInt64)`](https://clickhouse.com/docs/sql-reference/data-types/nullable)
**Examples**
**Usage example**
```
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB', 'invalid']) AS readable_sizes, parseReadableSizeOrNull(readable_sizes) AS sizes;
```
```
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
β invalid β α΄Ία΅α΄Έα΄Έ β
ββββββββββββββββββ΄ββββββββββ
```
## parseReadableSizeOrZero[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrZero "Direct link to parseReadableSizeOrZero")
Introduced in: v24.6.0
Given a string containing a byte size and `B`, `KiB`, `KB`, `MiB`, `MB`, etc. as a unit (i.e. [ISO/IEC 80000-13](https://en.wikipedia.org/wiki/ISO/IEC_80000) or decimal byte unit), this function returns the corresponding number of bytes. If the function is unable to parse the input value, it returns `0`.
The inverse operations of this function are [`formatReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize) and [`formatReadableDecimalSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize).
**Syntax**
```
parseReadableSizeOrZero(x)
```
**Arguments**
- `x` β Readable size with ISO/IEC 80000-13 or decimal byte unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the number of bytes, rounded up to the nearest integer, or `0` if unable to parse the input. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB', 'invalid']) AS readable_sizes, parseReadableSizeOrZero(readable_sizes) AS sizes;
```
```
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
β invalid β 0 β
ββββββββββββββββββ΄ββββββββββ
```
## parseTimeDelta[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseTimeDelta "Direct link to parseTimeDelta")
Introduced in: v22.7.0
Parse a sequence of numbers followed by something resembling a time unit.
The time delta string uses these time unit specifications:
- `years`, `year`, `yr`, `y`
- `months`, `month`, `mo`
- `weeks`, `week`, `w`
- `days`, `day`, `d`
- `hours`, `hour`, `hr`, `h`
- `minutes`, `minute`, `min`, `m`
- `seconds`, `second`, `sec`, `s`
- `milliseconds`, `millisecond`, `millisec`, `ms`
- `microseconds`, `microsecond`, `microsec`, `ΞΌs`, `Β΅s`, `us`
- `nanoseconds`, `nanosecond`, `nanosec`, `ns`
Multiple time units can be combined with separators (space, `;`, `-`, `+`, `,`, `:`).
The length of years and months are approximations: year is 365 days, month is 30.5 days.
**Syntax**
```
parseTimeDelta(timestr)
```
**Arguments**
- `timestr` β A sequence of numbers followed by something resembling a time unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The number of seconds. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Examples**
**Usage example**
```
SELECT parseTimeDelta('11s+22min')
```
```
ββparseTimeDelta('11s+22min')ββ
β 1331 β
βββββββββββββββββββββββββββββββ
```
**Complex time units**
```
SELECT parseTimeDelta('1yr2mo')
```
```
ββparseTimeDelta('1yr2mo')ββ
β 36806400 β
ββββββββββββββββββββββββββββ
```
## partitionId[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#partitionId "Direct link to partitionId")
Introduced in: v21.4.0
Computes the [partition ID](https://clickhouse.com/docs/engines/table-engines/mergetree-family/custom-partitioning-key).
Note
This function is slow and should not be called for large numbers of rows.
**Syntax**
```
partitionId(column1[, column2, ...])
```
**Aliases**: `partitionID`
**Arguments**
- `column1, column2, ...` β Column for which to return the partition ID.
**Returned value**
Returns the partition ID that the row belongs to. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
DROP TABLE IF EXISTS tab;
CREATE TABLE tab
(
i int,
j int
)
ENGINE = MergeTree
PARTITION BY i
ORDER BY tuple();
INSERT INTO tab VALUES (1, 1), (1, 2), (1, 3), (2, 4), (2, 5), (2, 6);
SELECT i, j, partitionId(i), _partition_id FROM tab ORDER BY i, j;
```
```
ββiββ¬βjββ¬βpartitionId(i)ββ¬β_partition_idββ
β 1 β 1 β 1 β 1 β
β 1 β 2 β 1 β 1 β
β 1 β 3 β 1 β 1 β
β 2 β 4 β 2 β 2 β
β 2 β 5 β 2 β 2 β
β 2 β 6 β 2 β 2 β
βββββ΄ββββ΄βββββββββββββββββ΄ββββββββββββββββ
```
## queryID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#queryID "Direct link to queryID")
Introduced in: v21.9.0
Returns the ID of the current query. Other parameters of a query can be extracted from field `query_id` in the [`system.query_log`](https://clickhouse.com/docs/operations/system-tables/query_log) table.
In contrast to [`initialQueryID`](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryID) function, `queryID` can return different results on different shards.
**Syntax**
```
queryID()
```
**Aliases**: `query_id`
**Arguments**
- None.
**Returned value**
Returns the ID of the current query. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT queryID() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
```
```
ββcount(DISTINCT t)ββ
β 3 β
βββββββββββββββββββββ
```
## revision[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#revision "Direct link to revision")
Introduced in: v22.7.0
Returns the current ClickHouse server revision.
**Syntax**
```
revision()
```
**Arguments**
- None.
**Returned value**
Returns the current ClickHouse server revision. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT revision()
```
```
ββrevision()ββ
β 54485 β
ββββββββββββββ
```
## rowNumberInAllBlocks[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#rowNumberInAllBlocks "Direct link to rowNumberInAllBlocks")
Introduced in: v1.1.0
Returns a unique row number for each row processed.
**Syntax**
```
rowNumberInAllBlocks()
```
**Arguments**
- None.
**Returned value**
Returns the ordinal number of the row in the data block starting from `0`. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT rowNumberInAllBlocks()
FROM
(
SELECT *
FROM system.numbers_mt
LIMIT 10
)
SETTINGS max_block_size = 2
```
```
ββrowNumberInAllBlocks()ββ
β 0 β
β 1 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 4 β
β 5 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 2 β
β 3 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 6 β
β 7 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 8 β
β 9 β
ββββββββββββββββββββββββββ
```
## rowNumberInBlock[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#rowNumberInBlock "Direct link to rowNumberInBlock")
Introduced in: v1.1.0
For each [block](https://clickhouse.com/docs/development/architecture#block) processed by `rowNumberInBlock`, returns the number of the current row.
The returned number starts from 0 for each block.
**Syntax**
```
rowNumberInBlock()
```
**Arguments**
- None.
**Returned value**
Returns the ordinal number of the row in the data block starting from `0`. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT rowNumberInBlock()
FROM
(
SELECT *
FROM system.numbers_mt
LIMIT 10
) SETTINGS max_block_size = 2
```
```
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
```
## runningAccumulate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningAccumulate "Direct link to runningAccumulate")
Introduced in: v1.1.0
Accumulates the states of an aggregate function for each row of a data block.
Deprecated
The state is reset for each new block of data. Due to this error-prone behavior the function has been deprecated, and you are advised to use [window functions](https://clickhouse.com/docs/sql-reference/window-functions) instead. You can use setting [`allow_deprecated_error_prone_window_functions`](https://clickhouse.com/docs/operations/settings/settings#allow_deprecated_error_prone_window_functions) to allow usage of this function.
**Syntax**
```
runningAccumulate(agg_state[, grouping])
```
**Arguments**
- `agg_state` β State of the aggregate function. [`AggregateFunction`](https://clickhouse.com/docs/sql-reference/data-types/aggregatefunction)
- `grouping` β Optional. Grouping key. The state of the function is reset if the `grouping` value is changed. It can be any of the supported data types for which the equality operator is defined. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the accumulated result for each row. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example with initializeAggregation**
```
WITH initializeAggregation('sumState', number) AS one_row_sum_state
SELECT
number,
finalizeAggregation(one_row_sum_state) AS one_row_sum,
runningAccumulate(one_row_sum_state) AS cumulative_sum
FROM numbers(5);
```
```
ββnumberββ¬βone_row_sumββ¬βcumulative_sumββ
β 0 β 0 β 0 β
β 1 β 1 β 1 β
β 2 β 2 β 3 β
β 3 β 3 β 6 β
β 4 β 4 β 10 β
ββββββββββ΄ββββββββββββββ΄βββββββββββββββββ
```
## runningConcurrency[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningConcurrency "Direct link to runningConcurrency")
Introduced in: v21.3.0
Calculates the number of concurrent events. Each event has a start time and an end time. The start time is included in the event, while the end time is excluded. Columns with a start time and an end time must be of the same data type. The function calculates the total number of active (concurrent) events for each event start time.
Requirements
Events must be ordered by the start time in ascending order. If this requirement is violated the function raises an exception. Every data block is processed separately. If events from different data blocks overlap then they can not be processed correctly.
Deprecated
It is advised to use [window functions](https://clickhouse.com/docs/sql-reference/window-functions) instead.
**Syntax**
```
runningConcurrency(start, end)
```
**Arguments**
- `start` β A column with the start time of events. [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`DateTime64`](https://clickhouse.com/docs/sql-reference/data-types/datetime64)
- `end` β A column with the end time of events. [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`DateTime64`](https://clickhouse.com/docs/sql-reference/data-types/datetime64)
**Returned value**
Returns the number of concurrent events at each event start time. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT start, runningConcurrency(start, end) FROM example_table;
```
```
βββββββstartββ¬βrunningConcurrency(start, end)ββ
β 2025-03-03 β 1 β
β 2025-03-06 β 2 β
β 2025-03-07 β 3 β
β 2025-03-11 β 2 β
ββββββββββββββ΄βββββββββββββββββββββββββββββββββ
```
## runningDifference[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifference "Direct link to runningDifference")
Introduced in: v1.1.0
Calculates the difference between two consecutive row values in the data block. Returns `0` for the first row, and for subsequent rows the difference to the previous row.
Deprecated
Only returns differences inside the currently processed data block. Because of this error-prone behavior, the function is deprecated. It is advised to use [window functions](https://clickhouse.com/docs/sql-reference/window-functions) instead.
You can use setting [`allow_deprecated_error_prone_window_functions`](https://clickhouse.com/docs/operations/settings/settings#allow_deprecated_error_prone_window_functions) to allow usage of this function.
The result of the function depends on the affected data blocks and the order of data in the block. The order of rows during calculation of `runningDifference()` can differ from the order of rows returned to the user. To prevent that you can create a subquery with [`ORDER BY`](https://clickhouse.com/docs/sql-reference/statements/select/order-by) and call the function from outside the subquery. Please note that the block size affects the result. The internal state of `runningDifference` state is reset for each new block.
**Syntax**
```
runningDifference(x)
```
**Arguments**
- `x` β Column for which to calculate the running difference. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the difference between consecutive values, with 0 for the first row.
**Examples**
**Usage example**
```
SELECT
EventID,
EventTime,
runningDifference(EventTime) AS delta
FROM
(
SELECT
EventID,
EventTime
FROM events
WHERE EventDate = '2025-11-24'
ORDER BY EventTime ASC
LIMIT 5
);
```
```
ββEventIDββ¬βββββββββββEventTimeββ¬βdeltaββ
β 1106 β 2025-11-24 00:00:04 β 0 β
β 1107 β 2025-11-24 00:00:05 β 1 β
β 1108 β 2025-11-24 00:00:05 β 0 β
β 1109 β 2025-11-24 00:00:09 β 4 β
β 1110 β 2025-11-24 00:00:10 β 1 β
βββββββββββ΄ββββββββββββββββββββββ΄ββββββββ
```
**Block size impact example**
```
SELECT
number,
runningDifference(number + 1) AS diff
FROM numbers(100000)
WHERE diff != 1;
```
```
ββnumberββ¬βdiffββ
β 0 β 0 β
ββββββββββ΄βββββββ
ββnumberββ¬βdiffββ
β 65536 β 0 β
ββββββββββ΄βββββββ
```
## runningDifferenceStartingWithFirstValue[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifferenceStartingWithFirstValue "Direct link to runningDifferenceStartingWithFirstValue")
Introduced in: v1.1.0
Calculates the difference between consecutive row values in a data block, but unlike [`runningDifference`](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifference), it returns the actual value of the first row instead of `0`.
Deprecated
Only returns differences inside the currently processed data block. Because of this error-prone behavior, the function is deprecated. It is advised to use [window functions](https://clickhouse.com/docs/sql-reference/window-functions) instead.
You can use setting `allow_deprecated_error_prone_window_functions` to allow usage of this function.
**Syntax**
```
runningDifferenceStartingWithFirstValue(x)
```
**Arguments**
- `x` β Column for which to calculate the running difference. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the difference between consecutive values, with the first row's value for the first row. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT
number,
runningDifferenceStartingWithFirstValue(number) AS diff
FROM numbers(5);
```
```
ββnumberββ¬βdiffββ
β 0 β 0 β
β 1 β 1 β
β 2 β 1 β
β 3 β 1 β
β 4 β 1 β
ββββββββββ΄βββββββ
```
## serverUUID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#serverUUID "Direct link to serverUUID")
Introduced in: v20.1.0
Returns the random and unique UUID (v4) generated when the server is first started. The UUID is persisted, i.e. the second, third, etc. server start return the same UUID.
**Syntax**
```
serverUUID()
```
**Arguments**
- None.
**Returned value**
Returns the random UUID of the server. [`UUID`](https://clickhouse.com/docs/sql-reference/data-types/uuid)
**Examples**
**Usage example**
```
SELECT serverUUID();
```
```
ββserverUUID()ββββββββββββββββββββββββββββββ
β 7ccc9260-000d-4d5c-a843-5459abaabb5f β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## shardCount[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#shardCount "Direct link to shardCount")
Introduced in: v21.9.0
Returns the total number of shards for a distributed query. If a query is not distributed then constant value `0` is returned.
**Syntax**
```
shardCount()
```
**Arguments**
- None.
**Returned value**
Returns the total number of shards or `0`. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
-- See shardNum() example above which also demonstrates shardCount()
CREATE TABLE shard_count_example (dummy UInt8)
ENGINE=Distributed(test_cluster_two_shards_localhost, system, one, dummy);
SELECT shardCount() FROM shard_count_example;
```
```
ββshardCount()ββ
β 2 β
β 2 β
ββββββββββββββββ
```
## shardNum[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#shardNum "Direct link to shardNum")
Introduced in: v21.9.0
Returns the index of a shard which processes a part of data in a distributed query. Indices begin from `1`. If a query is not distributed then a constant value `0` is returned.
**Syntax**
```
shardNum()
```
**Arguments**
- None.
**Returned value**
Returns the shard index or a constant `0`. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
CREATE TABLE shard_num_example (dummy UInt8)
ENGINE=Distributed(test_cluster_two_shards_localhost, system, one, dummy);
SELECT dummy, shardNum(), shardCount() FROM shard_num_example;
```
```
ββdummyββ¬βshardNum()ββ¬βshardCount()ββ
β 0 β 1 β 2 β
β 0 β 2 β 2 β
βββββββββ΄βββββββββββββ΄βββββββββββββββ
```
## showCertificate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#showCertificate "Direct link to showCertificate")
Introduced in: v22.6.0
Shows information about the current server's Secure Sockets Layer (SSL) certificate if it has been configured. See [Configuring TLS](https://clickhouse.com/docs/guides/sre/tls/configuring-tls) for more information on how to configure ClickHouse to use OpenSSL certificates to validate connections.
**Syntax**
```
showCertificate()
```
**Arguments**
- None.
**Returned value**
Returns map of key-value pairs relating to the configured SSL certificate. [`Map(String, String)`](https://clickhouse.com/docs/sql-reference/data-types/map)
**Examples**
**Usage example**
```
SELECT showCertificate() FORMAT LineAsString;
```
```
{'version':'1','serial_number':'2D9071D64530052D48308473922C7ADAFA85D6C5','signature_algo':'sha256WithRSAEncryption','issuer':'/CN=marsnet.local CA','not_before':'May 7 17:01:21 2024 GMT','not_after':'May 7 17:01:21 2025 GMT','subject':'/CN=chnode1','pkey_algo':'rsaEncryption'}
```
## sleep[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleep "Direct link to sleep")
Introduced in: v1.1.0
Pauses the execution of a query by the specified number of seconds. The function is primarily used for testing and debugging purposes.
The `sleep()` function should generally not be used in production environments, as it can negatively impact query performance and system responsiveness. However, it can be useful in the following scenarios:
1. **Testing**: When testing or benchmarking ClickHouse, you may want to simulate delays or introduce pauses to observe how the system behaves under certain conditions.
2. **Debugging**: If you need to examine the state of the system or the execution of a query at a specific point in time, you can use `sleep()` to introduce a pause, allowing you to inspect or collect relevant information.
3. **Simulation**: In some cases, you may want to simulate real-world scenarios where delays or pauses occur, such as network latency or external system dependencies.
Note
It's important to use the `sleep()` function judiciously and only when necessary, as it can potentially impact the overall performance and responsiveness of your ClickHouse system.
For security reasons, the function can only be executed in the default user profile (with `allow_sleep` enabled).
**Syntax**
```
sleep(seconds)
```
**Arguments**
- `seconds` β The number of seconds to pause the query execution to a maximum of 3 seconds. It can be a floating-point value to specify fractional seconds. [`const UInt*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`const Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns `0`. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
-- This query will pause for 2 seconds before completing.
-- During this time, no results will be returned, and the query will appear to be hanging or unresponsive.
SELECT sleep(2);
```
```
ββsleep(2)ββ
β 0 β
ββββββββββββ
1 row in set. Elapsed: 2.012 sec.
```
## sleepEachRow[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleepEachRow "Direct link to sleepEachRow")
Introduced in: v1.1.0
Pauses the execution of a query for a specified number of seconds for each row in the result set.
The `sleepEachRow()` function is primarily used for testing and debugging purposes, similar to the [`sleep()`](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleep) function. It allows you to simulate delays or introduce pauses in the processing of each row, which can be useful in scenarios such as:
1. **Testing**: When testing or benchmarking ClickHouse's performance under specific conditions, you can use `sleepEachRow()` to simulate delays or introduce pauses for each row processed.
2. **Debugging**: If you need to examine the state of the system or the execution of a query for each row processed, you can use `sleepEachRow()` to introduce pauses, allowing you to inspect or collect relevant information.
3. **Simulation**: In some cases, you may want to simulate real-world scenarios where delays or pauses occur for each row processed, such as when dealing with external systems or network latencies.
Note
Like the `sleep()` function, it's important to use `sleepEachRow()` judiciously and only when necessary, as it can significantly impact the overall performance and responsiveness of your ClickHouse system, especially when dealing with large result sets.
**Syntax**
```
sleepEachRow(seconds)
```
**Arguments**
- `seconds` β The number of seconds to pause the query execution for each row in the result set to a maximum of 3 seconds. It can be a floating-point value to specify fractional seconds. [`const UInt*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`const Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns `0` for each row. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
-- The output will be delayed, with a 0.5-second pause between each row.
SELECT number, sleepEachRow(0.5) FROM system.numbers LIMIT 5;
```
```
ββnumberββ¬βsleepEachRow(0.5)ββ
β 0 β 0 β
β 1 β 0 β
β 2 β 0 β
β 3 β 0 β
β 4 β 0 β
ββββββββββ΄ββββββββββββββββββββ
```
## structureToCapnProtoSchema[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#structureToCapnProtoSchema "Direct link to structureToCapnProtoSchema")
Introduced in: v23.8.0
Function that converts ClickHouse table structure to CapnProto format schema
**Syntax**
```
structureToCapnProtoSchema(table_structure, message)
```
**Arguments**
- None.
**Returned value**
**Examples**
**random**
```
SELECT structureToCapnProtoSchema('s String, x UInt32', 'MessageName') format TSVRaw
```
```
struct MessageName
{
s @0 : Data;
x @1 : UInt32;
}
```
## structureToProtobufSchema[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#structureToProtobufSchema "Direct link to structureToProtobufSchema")
Introduced in: v23.8.0
Converts a ClickHouse table structure to Protobuf format schema.
This function takes a ClickHouse table structure definition and converts it into a Protocol Buffers (Protobuf) schema definition in proto3 syntax. This is useful for generating Protobuf schemas that match your ClickHouse table structures for data interchange.
**Syntax**
```
structureToProtobufSchema(structure, message_name)
```
**Arguments**
- `structure` β ClickHouse table structure definition as a string (e.g., 'column1 Type1, column2 Type2'). [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `message_name` β Name for the Protobuf message type in the generated schema. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a Protobuf schema definition in proto3 syntax that corresponds to the input ClickHouse structure. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Converting ClickHouse structure to Protobuf schema**
```
SELECT structureToProtobufSchema('s String, x UInt32', 'MessageName') FORMAT TSVRaw;
```
```
syntax = "proto3";
message MessageName
{
bytes s = 1;
uint32 x = 2;
}
```
## tcpPort[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#tcpPort "Direct link to tcpPort")
Introduced in: v20.12.0
Returns the [native interface](https://clickhouse.com/docs/interfaces/tcp) TCP port number listened to by the server. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
tcpPort()
```
**Arguments**
- None.
**Returned value**
Returns the TCP port number. [`UInt16`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT tcpPort()
```
```
ββtcpPort()ββ
β 9000 β
βββββββββββββ
```
## throwIf[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#throwIf "Direct link to throwIf")
Introduced in: v1.1.0
Throw an exception if argument x is true. To use the `error_code` argument, configuration parameter `allow_custom_error_code_in_throw` must be enabled.
**Syntax**
```
throwIf(x[, message[, error_code]])
```
**Arguments**
- `x` β The condition to check. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
- `message` β Optional. Custom error message. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `error_code` β Optional. Custom error code. [`const Int8/16/32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns `0` if the condition is false, throws an exception if the condition is true. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT throwIf(number = 3, 'Too many') FROM numbers(10);
```
```
β Progress: 0.00 rows, 0.00 B (0.00 rows/s., 0.00 B/s.) Received exception from server (version 19.14.1):
Code: 395. DB::Exception: Received from localhost:9000. DB::Exception: Too many.
```
## toColumnTypeName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#toColumnTypeName "Direct link to toColumnTypeName")
Introduced in: v1.1.0
Returns the internal name of the data type of the given value. Unlike function [`toTypeName`](https://clickhouse.com/docs/sql-reference/functions/other-functions#toTypeName), the returned data type potentially includes internal wrapper columns like `Const` and `LowCardinality`.
**Syntax**
```
toColumnTypeName(value)
```
**Arguments**
- `value` β Value for which to return the internal data type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the internal data type used to represent the value. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT toColumnTypeName(CAST('2025-01-01 01:02:03' AS DateTime));
```
```
ββtoColumnTypeName(CAST('2025-01-01 01:02:03', 'DateTime'))ββ
β Const(UInt32) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## toTypeName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#toTypeName "Direct link to toTypeName")
Introduced in: v1.1.0
Returns the type name of the passed argument. If `NULL` is passed, the function returns type `Nullable(Nothing)`, which corresponds to ClickHouse's internal `NULL` representation.
**Syntax**
```
toTypeName(x)
```
**Arguments**
- `x` β A value of arbitrary type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the data type name of the input value. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT toTypeName(123)
```
```
ββtoTypeName(123)ββ
β UInt8 β
βββββββββββββββββββ
```
## transactionID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionID "Direct link to transactionID")
Introduced in: v22.6.0
Experimental feature.
[Learn more.](https://clickhouse.com/docs/beta-and-experimental-features#experimental-features)
Not supported in ClickHouse Cloud
Returns the ID of a transaction.
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your [configuration](https://clickhouse.com/docs/operations/configuration-files):
```
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
```
For more information see the page [Transactional (ACID) support](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
**Syntax**
```
transactionID()
```
**Arguments**
- None.
**Returned value**
Returns a tuple consisting of `start_csn`, `local_tid` and `host_id`.
- `start_csn`: Global sequential number, the newest commit timestamp that was seen when this transaction began.
- `local_tid`: Local sequential number that is unique for each transaction started by this host within a specific start\_csn.
- `host_id`: UUID of the host that has started this transaction. [`Tuple(UInt64, UInt64, UUID)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Usage example**
```
BEGIN TRANSACTION;
SELECT transactionID();
ROLLBACK;
```
```
ββtransactionID()βββββββββββββββββββββββββββββββββ
β (32,34,'0ee8b069-f2bb-4748-9eae-069c85b5252b') β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## transactionLatestSnapshot[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionLatestSnapshot "Direct link to transactionLatestSnapshot")
Introduced in: v22.6.0
Experimental feature.
[Learn more.](https://clickhouse.com/docs/beta-and-experimental-features#experimental-features)
Not supported in ClickHouse Cloud
Returns the newest snapshot (Commit Sequence Number) of a [transaction](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback) that is available for reading.
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your configuration:
```
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
```
For more information see the page [Transactional (ACID) support](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
**Syntax**
```
transactionLatestSnapshot()
```
**Arguments**
- None.
**Returned value**
Returns the latest snapshot (CSN) of a transaction. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
BEGIN TRANSACTION;
SELECT transactionLatestSnapshot();
ROLLBACK;
```
```
ββtransactionLatestSnapshot()ββ
β 32 β
βββββββββββββββββββββββββββββββ
```
## transactionOldestSnapshot[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionOldestSnapshot "Direct link to transactionOldestSnapshot")
Introduced in: v22.6.0
Experimental feature.
[Learn more.](https://clickhouse.com/docs/beta-and-experimental-features#experimental-features)
Not supported in ClickHouse Cloud
Returns the oldest snapshot (Commit Sequence Number) that is visible for some running [transaction](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your configuration:
```
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
```
For more information see the page [Transactional (ACID) support](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
**Syntax**
```
transactionOldestSnapshot()
```
**Arguments**
- None.
**Returned value**
Returns the oldest snapshot (CSN) of a transaction. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
BEGIN TRANSACTION;
SELECT transactionOldestSnapshot();
ROLLBACK;
```
```
ββtransactionOldestSnapshot()ββ
β 32 β
βββββββββββββββββββββββββββββββ
```
## transform[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transform "Direct link to transform")
Introduced in: v1.1.0
Transforms a value according to the explicitly defined mapping of some elements to other elements.
There are two variations of this function:
- `transform(x, array_from, array_to, default)` - transforms `x` using mapping arrays with a default value for unmatched elements
- `transform(x, array_from, array_to)` - same transformation but returns the original `x` if no match is found
The function searches for `x` in `array_from` and returns the corresponding element from `array_to` at the same index. If `x` is not found in `array_from`, it returns either the `default` value (4-parameter version) or the original `x` (3-parameter version). If multiple matching elements exist in `array_from`, it returns the element corresponding to the first match.
Requirements:
- `array_from` and `array_to` must have the same number of elements
- For 4-parameter version: `transform(T, Array(T), Array(U), U) -> U` where `T` and `U` can be different compatible types
- For 3-parameter version: `transform(T, Array(T), Array(T)) -> T` where all types must be the same
**Syntax**
```
transform(x, array_from, array_to[, default])
```
**Arguments**
- `x` β Value to transform. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
- `array_from` β Constant array of values to search for matches. [`Array((U)Int*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Decimal)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Float*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Date)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(DateTime)`](https://clickhouse.com/docs/sql-reference/data-types/array)
- `array_to` β Constant array of values to return for corresponding matches in `array_from`. [`Array((U)Int*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Decimal)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Float*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Date)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(DateTime)`](https://clickhouse.com/docs/sql-reference/data-types/array)
- `default` β Optional. Value to return if `x` is not found in `array_from`. If omitted, returns x unchanged. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
**Returned value**
Returns the corresponding value from `array_to` if x matches an element in `array_from`, otherwise returns default (if provided) or x (if default not provided). [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**transform(T, Array(T), Array(U), U) -\> U**
```
SELECT
transform(SearchEngineID, [2, 3], ['Yandex', 'Google'], 'Other') AS title,
count() AS c
FROM test.hits
WHERE SearchEngineID != 0
GROUP BY title
ORDER BY c DESC
```
```
ββtitleββββββ¬ββββββcββ
β Yandex β 498635 β
β Google β 229872 β
β Other β 104472 β
βββββββββββββ΄βββββββββ
```
**transform(T, Array(T), Array(T)) -\> T**
```
SELECT
transform(domain(Referer), ['yandex.ru', 'google.ru', 'vkontakte.ru'], ['www.yandex', 'example.com', 'vk.com']) AS s, count() AS c
FROM test.hits
GROUP BY domain(Referer)
ORDER BY count() DESC
LIMIT 10
```
```
ββsβββββββββββββββ¬βββββββcββ
β β 2906259 β
β www.yandex β 867767 β
β βββββββ.ru β 313599 β
β mail.yandex.ru β 107147 β
β ββββββ.ru β 100355 β
β βββββββββ.ru β 65040 β
β news.yandex.ru β 64515 β
β ββββββ.net β 59141 β
β example.com β 57316 β
ββββββββββββββββββ΄ββββββββββ
```
## uniqThetaIntersect[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaIntersect "Direct link to uniqThetaIntersect")
Introduced in: v22.9.0
Two uniqThetaSketch objects to do intersect calculation(set operation β©), the result is a new uniqThetaSketch.
**Syntax**
```
uniqThetaIntersect(uniqThetaSketch,uniqThetaSketch)
```
**Arguments**
- `uniqThetaSketch` β uniqThetaSketch object. [`Tuple`](https://clickhouse.com/docs/sql-reference/data-types/tuple) or [`Array`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
A new uniqThetaSketch containing the intersect result. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(uniqThetaIntersect(a, b)) AS a_intersect_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [1, 2]) AS a, arrayReduce('uniqThetaState', [2, 3, 4]) AS b);
```
```
ββa_intersect_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 1 β 2 β 3 β
βββββββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
```
## uniqThetaNot[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaNot "Direct link to uniqThetaNot")
Introduced in: v22.9.0
Two uniqThetaSketch objects to do a\_not\_b calculation(set operation Γ), the result is a new uniqThetaSketch.
**Syntax**
```
uniqThetaNot(uniqThetaSketch,uniqThetaSketch)
```
**Arguments**
- `uniqThetaSketch` β uniqThetaSketch object. [`Tuple`](https://clickhouse.com/docs/sql-reference/data-types/tuple) or [`Array`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns a new uniqThetaSketch containing the a\_not\_b result. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(uniqThetaNot(a, b)) AS a_not_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [2, 3, 4]) AS a, arrayReduce('uniqThetaState', [1, 2]) AS b);
```
```
ββa_not_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 2 β 3 β 2 β
βββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
```
## uniqThetaUnion[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaUnion "Direct link to uniqThetaUnion")
Introduced in: v22.9.0
Two uniqThetaSketch objects to do union calculation(set operation βͺ), the result is a new uniqThetaSketch.
**Syntax**
```
uniqThetaUnion(uniqThetaSketch,uniqThetaSketch)
```
**Arguments**
- `uniqThetaSketch` β uniqThetaSketch object. [`Tuple`](https://clickhouse.com/docs/sql-reference/data-types/tuple) or [`Array`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns a new uniqThetaSketch containing the union result. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(uniqThetaUnion(a, b)) AS a_union_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [1, 2]) AS a, arrayReduce('uniqThetaState', [2, 3, 4]) AS b);
```
```
ββa_union_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 4 β 2 β 3 β
βββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
```
## uptime[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uptime "Direct link to uptime")
Introduced in: v1.1.0
Returns the server's uptime in seconds. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
uptime()
```
**Arguments**
- None.
**Returned value**
Returns the server uptime in seconds. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT uptime() AS Uptime
```
```
ββUptimeββ
β 55867 β
ββββββββββ
```
## variantElement[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#variantElement "Direct link to variantElement")
Introduced in: v25.2.0
Extracts a column with specified type from a `Variant` column.
**Syntax**
```
variantElement(variant, type_name[, default_value])
```
**Arguments**
- `variant` β Variant column. [`Variant`](https://clickhouse.com/docs/sql-reference/data-types/variant)
- `type_name` β The name of the variant type to extract. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `default_value` β The default value that will be used if variant doesn't have variant with specified type. Can be any type. Optional. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a column with the specified variant type extracted from the Variant column. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
CREATE TABLE test (v Variant(UInt64, String, Array(UInt64))) ENGINE = Memory;
INSERT INTO test VALUES (NULL), (42), ('Hello, World!'), ([1, 2, 3]);
SELECT v, variantElement(v, 'String'), variantElement(v, 'UInt64'), variantElement(v, 'Array(UInt64)') FROM test;
```
```
ββvββββββββββββββ¬βvariantElement(v, 'String')ββ¬βvariantElement(v, 'UInt64')ββ¬βvariantElement(v, 'Array(UInt64)')ββ
β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β [] β
β 42 β α΄Ία΅α΄Έα΄Έ β 42 β [] β
β Hello, World! β Hello, World! β α΄Ία΅α΄Έα΄Έ β [] β
β [1,2,3] β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β [1,2,3] β
βββββββββββββββββ΄ββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββ
```
## variantType[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#variantType "Direct link to variantType")
Introduced in: v24.2.0
Returns the variant type name for each row of `Variant` column. If row contains NULL, it returns 'None' for it.
**Syntax**
```
variantType(variant)
```
**Arguments**
- `variant` β Variant column. [`Variant`](https://clickhouse.com/docs/sql-reference/data-types/variant)
**Returned value**
Returns an Enum column with variant type name for each row. [`Enum`](https://clickhouse.com/docs/sql-reference/data-types/enum)
**Examples**
**Usage example**
```
CREATE TABLE test (v Variant(UInt64, String, Array(UInt64))) ENGINE = Memory;
INSERT INTO test VALUES (NULL), (42), ('Hello, World!'), ([1, 2, 3]);
SELECT variantType(v) FROM test;
```
```
ββvariantType(v)ββ
β None β
β UInt64 β
β String β
β Array(UInt64) β
ββββββββββββββββββ
```
## version[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#version "Direct link to version")
Introduced in: v1.1.0
Returns the current version of ClickHouse as a string in the form: `major_version.minor_version.patch_version.number_of_commits_since_the_previous_stable_release`. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise, it produces a constant value.
**Syntax**
```
version()
```
**Arguments**
- None.
**Returned value**
Returns the current version of ClickHouse. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT version()
```
```
ββversion()ββ
β 24.2.1.1 β
βββββββββββββ
```
## visibleWidth[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#visibleWidth "Direct link to visibleWidth")
Introduced in: v1.1.0
Calculates the approximate width when outputting values to the console in text format (tab-separated). This function is used by the system to implement Pretty formats. `NULL` is represented as a string corresponding to `NULL` in Pretty formats.
**Syntax**
```
visibleWidth(x)
```
**Arguments**
- `x` β A value of any data type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the approximate width of the value when displayed in text format. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Calculate visible width of NULL**
```
SELECT visibleWidth(NULL)
```
```
ββvisibleWidth(NULL)ββ
β 4 β
ββββββββββββββββββββββ
```
## zookeeperSessionUptime[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#zookeeperSessionUptime "Direct link to zookeeperSessionUptime")
Introduced in: v21.11.0
Returns the uptime of the current ZooKeeper session in seconds.
**Syntax**
```
zookeeperSessionUptime()
```
**Arguments**
- None.
**Returned value**
Returns the uptime of the current ZooKeeper session in seconds. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT zookeeperSessionUptime();
```
```
ββzookeeperSessionUptime()ββ
β 286 β
ββββββββββββββββββββββββββββ
```
[Previous NumericIndexedVector](https://clickhouse.com/docs/sql-reference/functions/numeric-indexed-vector-functions)
[Next Random number](https://clickhouse.com/docs/sql-reference/functions/random-functions)
- [FQDN](https://clickhouse.com/docs/sql-reference/functions/other-functions#FQDN)
- [MACNumToString](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACNumToString)
- [MACStringToNum](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACStringToNum)
- [MACStringToOUI](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACStringToOUI)
- [authenticatedUser](https://clickhouse.com/docs/sql-reference/functions/other-functions#authenticatedUser)
- [bar](https://clickhouse.com/docs/sql-reference/functions/other-functions#bar)
- [blockNumber](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockNumber)
- [blockSerializedSize](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockSerializedSize)
- [blockSize](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockSize)
- [buildId](https://clickhouse.com/docs/sql-reference/functions/other-functions#buildId)
- [byteSize](https://clickhouse.com/docs/sql-reference/functions/other-functions#byteSize)
- [catboostEvaluate](https://clickhouse.com/docs/sql-reference/functions/other-functions#catboostEvaluate)
- [colorOKLABToSRGB](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorOKLABToSRGB)
- [colorOKLCHToSRGB](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorOKLCHToSRGB)
- [colorSRGBToOKLAB](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLAB)
- [colorSRGBToOKLCH](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLCH)
- [connectionId](https://clickhouse.com/docs/sql-reference/functions/other-functions#connectionId)
- [countDigits](https://clickhouse.com/docs/sql-reference/functions/other-functions#countDigits)
- [currentDatabase](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentDatabase)
- [currentProfiles](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentProfiles)
- [currentQueryID](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentQueryID)
- [currentRoles](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentRoles)
- [currentSchemas](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentSchemas)
- [currentUser](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentUser)
- [defaultProfiles](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultProfiles)
- [defaultRoles](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultRoles)
- [defaultValueOfArgumentType](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultValueOfArgumentType)
- [defaultValueOfTypeName](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultValueOfTypeName)
- [displayName](https://clickhouse.com/docs/sql-reference/functions/other-functions#displayName)
- [dumpColumnStructure](https://clickhouse.com/docs/sql-reference/functions/other-functions#dumpColumnStructure)
- [enabledProfiles](https://clickhouse.com/docs/sql-reference/functions/other-functions#enabledProfiles)
- [enabledRoles](https://clickhouse.com/docs/sql-reference/functions/other-functions#enabledRoles)
- [errorCodeToName](https://clickhouse.com/docs/sql-reference/functions/other-functions#errorCodeToName)
- [file](https://clickhouse.com/docs/sql-reference/functions/other-functions#file)
- [filesystemAvailable](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemAvailable)
- [filesystemCapacity](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemCapacity)
- [filesystemUnreserved](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemUnreserved)
- [finalizeAggregation](https://clickhouse.com/docs/sql-reference/functions/other-functions#finalizeAggregation)
- [flipCoordinates](https://clickhouse.com/docs/sql-reference/functions/other-functions#flipCoordinates)
- [formatQuery](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuery)
- [formatQueryOrNull](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQueryOrNull)
- [formatQuerySingleLine](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuerySingleLine)
- [formatQuerySingleLineOrNull](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuerySingleLineOrNull)
- [formatReadableDecimalSize](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize)
- [formatReadableQuantity](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableQuantity)
- [formatReadableSize](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize)
- [formatReadableTimeDelta](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableTimeDelta)
- [fuzzQuery](https://clickhouse.com/docs/sql-reference/functions/other-functions#fuzzQuery)
- [generateRandomStructure](https://clickhouse.com/docs/sql-reference/functions/other-functions#generateRandomStructure)
- [generateSerialID](https://clickhouse.com/docs/sql-reference/functions/other-functions#generateSerialID)
- [getClientHTTPHeader](https://clickhouse.com/docs/sql-reference/functions/other-functions#getClientHTTPHeader)
- [getMacro](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMacro)
- [getMaxTableNameLengthForDatabase](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMaxTableNameLengthForDatabase)
- [getMergeTreeSetting](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMergeTreeSetting)
- [getOSKernelVersion](https://clickhouse.com/docs/sql-reference/functions/other-functions#getOSKernelVersion)
- [getServerPort](https://clickhouse.com/docs/sql-reference/functions/other-functions#getServerPort)
- [getServerSetting](https://clickhouse.com/docs/sql-reference/functions/other-functions#getServerSetting)
- [getSetting](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSetting)
- [getSettingOrDefault](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSettingOrDefault)
- [getSizeOfEnumType](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSizeOfEnumType)
- [getSubcolumn](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSubcolumn)
- [getTypeSerializationStreams](https://clickhouse.com/docs/sql-reference/functions/other-functions#getTypeSerializationStreams)
- [globalVariable](https://clickhouse.com/docs/sql-reference/functions/other-functions#globalVariable)
- [hasColumnInTable](https://clickhouse.com/docs/sql-reference/functions/other-functions#hasColumnInTable)
- [hasThreadFuzzer](https://clickhouse.com/docs/sql-reference/functions/other-functions#hasThreadFuzzer)
- [hostName](https://clickhouse.com/docs/sql-reference/functions/other-functions#hostName)
- [icebergBucket](https://clickhouse.com/docs/sql-reference/functions/other-functions#icebergBucket)
- [icebergTruncate](https://clickhouse.com/docs/sql-reference/functions/other-functions#icebergTruncate)
- [identity](https://clickhouse.com/docs/sql-reference/functions/other-functions#identity)
- [ignore](https://clickhouse.com/docs/sql-reference/functions/other-functions#ignore)
- [indexHint](https://clickhouse.com/docs/sql-reference/functions/other-functions#indexHint)
- [initialQueryID](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryID)
- [initialQueryStartTime](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryStartTime)
- [initializeAggregation](https://clickhouse.com/docs/sql-reference/functions/other-functions#initializeAggregation)
- [isConstant](https://clickhouse.com/docs/sql-reference/functions/other-functions#isConstant)
- [isDecimalOverflow](https://clickhouse.com/docs/sql-reference/functions/other-functions#isDecimalOverflow)
- [joinGet](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGet)
- [joinGetOrNull](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGetOrNull)
- [lowCardinalityIndices](https://clickhouse.com/docs/sql-reference/functions/other-functions#lowCardinalityIndices)
- [lowCardinalityKeys](https://clickhouse.com/docs/sql-reference/functions/other-functions#lowCardinalityKeys)
- [materialize](https://clickhouse.com/docs/sql-reference/functions/other-functions#materialize)
- [minSampleSizeContinuous](https://clickhouse.com/docs/sql-reference/functions/other-functions#minSampleSizeContinuous)
- [minSampleSizeConversion](https://clickhouse.com/docs/sql-reference/functions/other-functions#minSampleSizeConversion)
- [neighbor](https://clickhouse.com/docs/sql-reference/functions/other-functions#neighbor)
- [normalizeQuery](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizeQuery)
- [normalizeQueryKeepNames](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizeQueryKeepNames)
- [normalizedQueryHash](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHash)
- [normalizedQueryHashKeepNames](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHashKeepNames)
- [parseReadableSize](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize)
- [parseReadableSizeOrNull](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrNull)
- [parseReadableSizeOrZero](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrZero)
- [parseTimeDelta](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseTimeDelta)
- [partitionId](https://clickhouse.com/docs/sql-reference/functions/other-functions#partitionId)
- [queryID](https://clickhouse.com/docs/sql-reference/functions/other-functions#queryID)
- [revision](https://clickhouse.com/docs/sql-reference/functions/other-functions#revision)
- [rowNumberInAllBlocks](https://clickhouse.com/docs/sql-reference/functions/other-functions#rowNumberInAllBlocks)
- [rowNumberInBlock](https://clickhouse.com/docs/sql-reference/functions/other-functions#rowNumberInBlock)
- [runningAccumulate](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningAccumulate)
- [runningConcurrency](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningConcurrency)
- [runningDifference](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifference)
- [runningDifferenceStartingWithFirstValue](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifferenceStartingWithFirstValue)
- [serverUUID](https://clickhouse.com/docs/sql-reference/functions/other-functions#serverUUID)
- [shardCount](https://clickhouse.com/docs/sql-reference/functions/other-functions#shardCount)
- [shardNum](https://clickhouse.com/docs/sql-reference/functions/other-functions#shardNum)
- [showCertificate](https://clickhouse.com/docs/sql-reference/functions/other-functions#showCertificate)
- [sleep](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleep)
- [sleepEachRow](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleepEachRow)
- [structureToCapnProtoSchema](https://clickhouse.com/docs/sql-reference/functions/other-functions#structureToCapnProtoSchema)
- [structureToProtobufSchema](https://clickhouse.com/docs/sql-reference/functions/other-functions#structureToProtobufSchema)
- [tcpPort](https://clickhouse.com/docs/sql-reference/functions/other-functions#tcpPort)
- [throwIf](https://clickhouse.com/docs/sql-reference/functions/other-functions#throwIf)
- [toColumnTypeName](https://clickhouse.com/docs/sql-reference/functions/other-functions#toColumnTypeName)
- [toTypeName](https://clickhouse.com/docs/sql-reference/functions/other-functions#toTypeName)
- [transactionID](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionID)
- [transactionLatestSnapshot](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionLatestSnapshot)
- [transactionOldestSnapshot](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionOldestSnapshot)
- [transform](https://clickhouse.com/docs/sql-reference/functions/other-functions#transform)
- [uniqThetaIntersect](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaIntersect)
- [uniqThetaNot](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaNot)
- [uniqThetaUnion](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaUnion)
- [uptime](https://clickhouse.com/docs/sql-reference/functions/other-functions#uptime)
- [variantElement](https://clickhouse.com/docs/sql-reference/functions/other-functions#variantElement)
- [variantType](https://clickhouse.com/docs/sql-reference/functions/other-functions#variantType)
- [version](https://clickhouse.com/docs/sql-reference/functions/other-functions#version)
- [visibleWidth](https://clickhouse.com/docs/sql-reference/functions/other-functions#visibleWidth)
- [zookeeperSessionUptime](https://clickhouse.com/docs/sql-reference/functions/other-functions#zookeeperSessionUptime)
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- [Overview](https://clickhouse.com/docs/sql-reference/functions/overview)
- [AI](https://clickhouse.com/docs/sql-reference/functions/ai-functions)
- [Arithmetic](https://clickhouse.com/docs/sql-reference/functions/arithmetic-functions)
- [Arrays](https://clickhouse.com/docs/sql-reference/functions/array-functions)
- [arrayJoin](https://clickhouse.com/docs/sql-reference/functions/array-join)
- [Bit](https://clickhouse.com/docs/sql-reference/functions/bit-functions)
- [Bitmap](https://clickhouse.com/docs/sql-reference/functions/bitmap-functions)
- [Comparison](https://clickhouse.com/docs/sql-reference/functions/comparison-functions)
- [Conditional](https://clickhouse.com/docs/sql-reference/functions/conditional-functions)
- [Dates and time](https://clickhouse.com/docs/sql-reference/functions/date-time-functions)
- [Distance](https://clickhouse.com/docs/sql-reference/functions/distance-functions)
- [Embedded dictionary](https://clickhouse.com/docs/sql-reference/functions/ym-dict-functions)
- [Encoding](https://clickhouse.com/docs/sql-reference/functions/encoding-functions)
- [Encryption](https://clickhouse.com/docs/sql-reference/functions/encryption-functions)
- [Dictionaries](https://clickhouse.com/docs/sql-reference/functions/ext-dict-functions)
- [Files](https://clickhouse.com/docs/sql-reference/functions/files)
- [Financial](https://clickhouse.com/docs/sql-reference/functions/financial-functions)
- [Nullable](https://clickhouse.com/docs/sql-reference/functions/functions-for-nulls)
- GeometryβΌ
- [Hash](https://clickhouse.com/docs/sql-reference/functions/hash-functions)
- [IN Operator](https://clickhouse.com/docs/sql-reference/functions/in-functions)
- [Introspection](https://clickhouse.com/docs/sql-reference/functions/introspection)
- [IP Addresses](https://clickhouse.com/docs/sql-reference/functions/ip-address-functions)
- [JSON](https://clickhouse.com/docs/sql-reference/functions/json-functions)
- [Logical](https://clickhouse.com/docs/sql-reference/functions/logical-functions)
- [Machine Learning](https://clickhouse.com/docs/sql-reference/functions/machine-learning-functions)
- [Mathematical](https://clickhouse.com/docs/sql-reference/functions/math-functions)
- [NLP](https://clickhouse.com/docs/sql-reference/functions/nlp-functions)
- [NumericIndexedVector](https://clickhouse.com/docs/sql-reference/functions/numeric-indexed-vector-functions)
- [Other](https://clickhouse.com/docs/sql-reference/functions/other-functions)
- [Random number](https://clickhouse.com/docs/sql-reference/functions/random-functions)
- [Rounding](https://clickhouse.com/docs/sql-reference/functions/rounding-functions)
- [String splitting](https://clickhouse.com/docs/sql-reference/functions/splitting-merging-functions)
- [String](https://clickhouse.com/docs/sql-reference/functions/string-functions)
- [String replacement](https://clickhouse.com/docs/sql-reference/functions/string-replace-functions)
- [String search](https://clickhouse.com/docs/sql-reference/functions/string-search-functions)
- [TimeSeries](https://clickhouse.com/docs/sql-reference/functions/time-series-functions)
- [Time window](https://clickhouse.com/docs/sql-reference/functions/time-window-functions)
- [Tuples](https://clickhouse.com/docs/sql-reference/functions/tuple-functions)
- [Maps](https://clickhouse.com/docs/sql-reference/functions/tuple-map-functions)
- [Type conversion](https://clickhouse.com/docs/sql-reference/functions/type-conversion-functions)
- [UDF](https://clickhouse.com/docs/sql-reference/functions/udf)
- [ULIDs](https://clickhouse.com/docs/sql-reference/functions/ulid-functions)
- [uniqTheta](https://clickhouse.com/docs/sql-reference/functions/uniqtheta-functions)
- [URLs](https://clickhouse.com/docs/sql-reference/functions/url-functions)
- [UUIDs](https://clickhouse.com/docs/sql-reference/functions/uuid-functions)
- [WebAssembly UDFs](https://clickhouse.com/docs/sql-reference/functions/wasm_udf)
- Aggregate functionsβΌ
- Table functionsβΌ
- Window functionsβΌ
- FormatsβΌ
- [Data Lakes](https://clickhouse.com/docs/sql-reference/datalakes) |
| Readable Markdown | Note
The function documentation below is generated from the `system.functions` system table.
## FQDN[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#FQDN "Direct link to FQDN")
Introduced in: v20.1.0
Returns the fully qualified domain name of the ClickHouse server.
**Syntax**
```
FQDN()
```
**Aliases**: `fullHostName`
**Arguments**
- None.
**Returned value**
Returns the fully qualified domain name of the ClickHouse server. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT fqdn()
```
Response
```
ββFQDN()βββββββββββββββββββββββββββ
β clickhouse.us-east-2.internal β
βββββββββββββββββββββββββββββββββββ
```
## MACNumToString[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACNumToString "Direct link to MACNumToString")
Introduced in: v1.1.0
Interprets a [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) number as a MAC address in big endian format. Returns the corresponding MAC address in format `AA:BB:CC:DD:EE:FF` (colon-separated numbers in hexadecimal form) as string.
**Syntax**
```
MACNumToString(num)
```
**Arguments**
- `num` β UInt64 number. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a MAC address in format AA:BB:CC:DD:EE:FF. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT MACNumToString(149809441867716) AS mac_address;
```
Response
```
ββmac_addressββββββββ
β 88:00:11:22:33:44 β
βββββββββββββββββββββ
```
## MACStringToNum[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACStringToNum "Direct link to MACStringToNum")
Introduced in: v1.1.0
The inverse function of MACNumToString. If the MAC address has an invalid format, it returns 0.
**Syntax**
```
MACStringToNum(s)
```
**Arguments**
- `s` β MAC address string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a UInt64 number. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT MACStringToNum('01:02:03:04:05:06') AS mac_numeric;
```
Response
```
1108152157446
```
## MACStringToOUI[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#MACStringToOUI "Direct link to MACStringToOUI")
Introduced in: v1.1.0
Given a MAC address in format AA:BB:CC:DD:EE:FF (colon-separated numbers in hexadecimal form), returns the first three octets as a UInt64 number. If the MAC address has an invalid format, it returns 0.
**Syntax**
```
MACStringToOUI(s)
```
**Arguments**
- `s` β MAC address string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
First three octets as UInt64 number. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT MACStringToOUI('00:50:56:12:34:56') AS oui;
```
Response
```
20566
```
## authenticatedUser[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#authenticatedUser "Direct link to authenticatedUser")
Introduced in: v25.11.0
If the session user has been switched using the EXECUTE AS command, this function returns the name of the original user that was used for authentication and creating the session. Alias: authUser()
**Syntax**
```
authenticatedUser()
```
**Aliases**: `authUser`
**Arguments**
- None.
**Returned value**
The name of the authenticated user. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
EXECUTE as u1;
SELECT currentUser(), authenticatedUser();
```
Response
```
ββcurrentUser()ββ¬βauthenticatedUser()ββ
β u1 β default β
βββββββββββββββββ΄ββββββββββββββββββββββ
```
## bar[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#bar "Direct link to bar")
Introduced in: v1.1.0
Builds a bar chart. Draws a band with width proportional to (x - min) and equal to width characters when x = max. The band is drawn with accuracy to one eighth of a symbol.
**Syntax**
```
bar(x, min, max[, width])
```
**Arguments**
- `x` β Size to display. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `min` β The minimum value. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `max` β The maximum value. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `width` β Optional. The width of the bar in characters. The default is `80`. [`const (U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`const Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`const Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns a unicode-art bar string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT
toHour(EventTime) AS h,
count() AS c,
bar(c, 0, 600000, 20) AS bar
FROM test.hits
GROUP BY h
ORDER BY h ASC
```
Response
```
βββhββ¬ββββββcββ¬βbarβββββββββββββββββ
β 0 β 292907 β ββββββββββ β
β 1 β 180563 β ββββββ β
β 2 β 114861 β ββββ β
β 3 β 85069 β βββ β
β 4 β 68543 β βββ β
β 5 β 78116 β βββ β
β 6 β 113474 β ββββ β
β 7 β 170678 β ββββββ β
β 8 β 278380 β ββββββββββ β
β 9 β 391053 β βββββββββββββ β
β 10 β 457681 β ββββββββββββββββ β
β 11 β 493667 β βββββββββββββββββ β
β 12 β 509641 β βββββββββββββββββ β
β 13 β 522947 β ββββββββββββββββββ β
β 14 β 539954 β ββββββββββββββββββ β
β 15 β 528460 β ββββββββββββββββββ β
β 16 β 539201 β ββββββββββββββββββ β
β 17 β 523539 β ββββββββββββββββββ β
β 18 β 506467 β βββββββββββββββββ β
β 19 β 520915 β ββββββββββββββββββ β
β 20 β 521665 β ββββββββββββββββββ β
β 21 β 542078 β ββββββββββββββββββ β
β 22 β 493642 β βββββββββββββββββ β
β 23 β 400397 β ββββββββββββββ β
ββββββ΄βββββββββ΄βββββββββββββββββββββ
```
## blockNumber[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockNumber "Direct link to blockNumber")
Introduced in: v1.1.0
Returns a monotonically increasing sequence number of the [block](https://clickhouse.com/docs/development/architecture#block) containing the row. The returned block number is updated on a best-effort basis, i.e. it may not be fully accurate.
**Syntax**
```
blockNumber()
```
**Arguments**
- None.
**Returned value**
Sequence number of the data block where the row is located. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Basic usage**
Query
```
SELECT blockNumber()
FROM
(
SELECT *
FROM system.numbers
LIMIT 10
) SETTINGS max_block_size = 2
```
Response
```
ββblockNumber()ββ
β 7 β
β 7 β
βββββββββββββββββ
ββblockNumber()ββ
β 8 β
β 8 β
βββββββββββββββββ
ββblockNumber()ββ
β 9 β
β 9 β
βββββββββββββββββ
ββblockNumber()ββ
β 10 β
β 10 β
βββββββββββββββββ
ββblockNumber()ββ
β 11 β
β 11 β
βββββββββββββββββ
```
## blockSerializedSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockSerializedSize "Direct link to blockSerializedSize")
Introduced in: v20.3.0
Returns the uncompressed size in bytes of a block of values on disk.
**Syntax**
```
blockSerializedSize(x1[, x2[, ...]])
```
**Arguments**
- `x1[, x2, ...]` β Any number of values for which to get the uncompressed size of the block. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the number of bytes that will be written to disk for a block of values without compression. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT blockSerializedSize(maxState(1)) AS x;
```
Response
```
ββxββ
β 2 β
βββββ
```
## blockSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#blockSize "Direct link to blockSize")
Introduced in: v1.1.0
In ClickHouse, queries are processed in [blocks](https://clickhouse.com/docs/development/architecture#block) (chunks). This function returns the size (row count) of the block the function is called on.
**Syntax**
```
blockSize()
```
**Arguments**
- None.
**Returned value**
Returns the number of rows in the current block. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT blockSize()
FROM system.numbers LIMIT 5
```
Response
```
ββblockSize()ββ
β 5 β
β 5 β
β 5 β
β 5 β
β 5 β
βββββββββββββββ
```
## buildId[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#buildId "Direct link to buildId")
Introduced in: v20.5.0
Returns the build ID generated by a compiler for the running ClickHouse server binary. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
buildId()
```
**Arguments**
- None.
**Returned value**
Returns the build ID. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
Query
```
SELECT buildId()
```
Response
```
ββbuildId()βββββββββββββββββββββββββββββββββ
β AB668BEF095FAA6BD26537F197AC2AF48A927FB4 β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## byteSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#byteSize "Direct link to byteSize")
Introduced in: v21.1.0
Returns an estimation of the uncompressed byte size of its arguments in memory. For `String` arguments, the function returns the string length + 8 (length). If the function has multiple arguments, the function accumulates their byte sizes.
**Syntax**
```
byteSize(arg1[, arg2, ...])
```
**Arguments**
- `arg1[, arg2, ...]` β Values of any data type for which to estimate the uncompressed byte size. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns an estimation of the byte size of the arguments in memory. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
Query
```
SELECT byteSize('string')
```
Response
```
ββbyteSize('string')ββ
β 15 β
ββββββββββββββββββββββ
```
**Multiple arguments**
Query
```
SELECT byteSize(NULL, 1, 0.3, '')
```
Response
```
ββbyteSize(NULL, 1, 0.3, '')ββ
β 19 β
ββββββββββββββββββββββββββββββ
```
## catboostEvaluate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#catboostEvaluate "Direct link to catboostEvaluate")
Introduced in: v22.9.0
Evaluate an external catboost model. [CatBoost](https://catboost.ai/) is an open-source gradient boosting library developed by Yandex for machine learning. Accepts a path to a catboost model and model arguments (features).
**Prerequisites**
1. Build the catboost evaluation library
Before evaluating catboost models, the `libcatboostmodel.<so|dylib>` library must be made available. See [CatBoost documentation](https://catboost.ai/docs/concepts/c-plus-plus-api_dynamic-c-pluplus-wrapper.html) how to compile it.
Next, specify the path to `libcatboostmodel.<so|dylib>` in the clickhouse configuration:
```
<clickhouse>
...
<catboost_lib_path>/path/to/libcatboostmodel.so</catboost_lib_path>
...
</clickhouse>
```
For security and isolation reasons, the model evaluation does not run in the server process but in the clickhouse-library-bridge process. At the first execution of `catboostEvaluate()`, the server starts the library bridge process if it is not running already. Both processes communicate using a HTTP interface. By default, port `9012` is used. A different port can be specified as follows - this is useful if port `9012` is already assigned to a different service.
```
<library_bridge>
<port>9019</port>
</library_bridge>
```
1. Train a catboost model using libcatboost
See [Training and applying models](https://catboost.ai/docs/features/training.html#training) for how to train catboost models from a training data set.
**Syntax**
```
catboostEvaluate(path_to_model, feature_1[, feature_2, ..., feature_n])
```
**Arguments**
- `path_to_model` β Path to catboost model. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `feature` β One or more model features/arguments. [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns the model evaluation result. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Examples**
**catboostEvaluate**
Query
```
SELECT catboostEvaluate('/root/occupy.bin', Temperature, Humidity, Light, CO2, HumidityRatio) AS prediction FROM occupancy LIMIT 1
```
Response
```
4.695691092573497
```
## colorOKLABToSRGB[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorOKLABToSRGB "Direct link to colorOKLABToSRGB")
Introduced in: v26.2.0
Converts a color from the OKLab perceptual color space to the sRGB color space.
The input color is specified in the OKLab color space. If the input values are outside the typical OKLab ranges, the result is implementation-defined.
OKLab uses three components:
- L: perceptual lightness (typically in the range \[0..1\])
- a: green-red opponent axis
- b: blue-yellow opponent axis
The a and b components are theoretically unbounded, but in practice are between -0.4 and 0.4. OKLab is designed to be perceptually uniform while remaining inexpensive to compute.
The conversion is intended to be the inverse of colorSRGBToOKLAB and consists of the following stages:
1. Conversion from OKLab to linear sRGB.
2. Conversion from linear sRGB to gamma-encoded sRGB.
The optional gamma argument specifies the exponent used when converting from linear sRGB to gamma-encoded RGB values. If not specified, a default gamma value is used for consistency with colorSRGBToOKLAB.
For more information about the OKLab color space and its relationship to sRGB, see <https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/color_value/oklab> .
**Syntax**
```
colorOKLABToSRGB(tuple [, gamma])
```
**Arguments**
- `tuple` β A tuple of three numeric values `L`, `a`, `b`, where `L` is in the range `[0...1]`. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. The exponent that is used to transform linear sRGB back to sRGB by applying `(x ^ (1 / gamma)) * 255` for each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (R, G, B) representing sRGB color values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert OKLAB to sRGB (Float)**
Query
```
SELECT colorOKLABToSRGB((0.4466, 0.0991, 0.44)) AS rgb;
```
Response
```
ββrgbβββββββββββββββββββββββ
β (198.07056923258935,0,0) β
ββββββββββββββββββββββββββββ
```
**Convert OKLAB to sRGB (UInt8)**
Query
```
WITH colorOKLABToSRGB((0.7, 0.1, 0.54)) AS t
SELECT tuple(toUInt8(t.1), toUInt8(t.2), toUInt8(t.3)) AS RGB;
```
Response
```
ββRGBβββββββββββ
β (255,0,0) β
ββββββββββββββββ
```
## colorOKLCHToSRGB[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorOKLCHToSRGB "Direct link to colorOKLCHToSRGB")
Introduced in: v25.7.0
Converts a colour from the **OKLCH** perceptual colour space to the familiar **sRGB** colour space.
If `L` is outside the range `[0...1]`, `C` is negative, or `H` is outside the range `[0...360]`, the result is implementation-defined.
Note
**OKLCH** is a cylindrical version of the OKLab colour space. It's three coordinates are `L` (the lightness in the range `[0...1]`), `C` (chroma `>= 0`) and `H` (hue in degrees from `[0...360]`). OKLab/OKLCH is designed to be perceptually uniform while remaining cheap to compute.
The conversion is the inverse of [`colorSRGBToOKLCH`](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLCH):
1. OKLCH to OKLab.
2. OKLab to Linear sRGB
3. Linear sRGB to sRGB
The second argument gamma is used at the last stage.
For references of colors in OKLCH space, and how they correspond to sRGB colors please see <https://oklch.com/>.
**Syntax**
```
colorOKLCHToSRGB(tuple [, gamma])
```
**Arguments**
- `tuple` β A tuple of three numeric values `L`, `C`, `H`, where `L` is in the range `[0...1]`, `C >= 0` and `H` is in the range `[0...360]`. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. The exponent that is used to transform linear sRGB back to sRGB by applying `(x ^ (1 / gamma)) * 255` for each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (R, G, B) representing sRGB color values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert OKLCH to sRGB**
```
SELECT colorOKLCHToSRGB((0.6, 0.12, 40)) AS rgb;
```
```
ββrgbββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (186.02058688365264,100.68677189684993,71.67819977081575) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
**Convert OKLCH to sRGB (UInt8)**
```
WITH colorOKLCHToSRGB((0.6, 0.12, 40)) AS t
SELECT tuple(toUInt8(t.1), toUInt8(t.2), toUInt8(t.3)) AS RGB;
```
```
ββRGBβββββββββββ
β (186,100,71) β
ββββββββββββββββ
```
## colorSRGBToOKLAB[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLAB "Direct link to colorSRGBToOKLAB")
Introduced in: v26.2.0
Converts a colour encoded in the **sRGB** colour space to the perceptually uniform **OKLAB** colour space.
If any input channel is outside `[0...255]` or the gamma value is non-positive, the behaviour is implementation-defined.
Note
**OKLAB** is a perceptually uniform color space. Its three coordinates are `L` (the lightness in the range `[0...1]`), `a (Green-Red axis)` and `b (Blue-Yellow axis)`. OKLab is designed to be perceptually uniform while remaining cheap to compute.
The conversion consists of two stages:
1. sRGB to Linear sRGB
2. Linear sRGB to OKLab
**Syntax**
```
colorSRGBToOKLAB(tuple[, gamma])
```
**Arguments**
- `tuple` β Tuple of three values R, G, B in the range `[0...255]`. [`Tuple(UInt8, UInt8, UInt8)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. Exponent that is used to linearize sRGB by applying `(x / 255)^gamma` to each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (L, a, b) representing the OKLAB color space values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert sRGB to OKLAB**
```
SELECT colorSRGBToOKLAB((128, 64, 32), 2.2) AS lab;
```
```
ββlabβββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (0.4436238384931984,0.07266246769242975,0.07500108778529994) β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## colorSRGBToOKLCH[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#colorSRGBToOKLCH "Direct link to colorSRGBToOKLCH")
Introduced in: v25.7.0
Converts a colour encoded in the **sRGB** colour space to the perceptually uniform **OKLCH** colour space.
If any input channel is outside `[0...255]` or the gamma value is non-positive, the behaviour is implementation-defined.
Note
**OKLCH** is a cylindrical version of the OKLab colour space. It's three coordinates are `L` (the lightness in the range `[0...1]`), `C` (chroma `>= 0`) and `H` (the hue in degrees from `[0...360]`). OKLab/OKLCH is designed to be perceptually uniform while remaining cheap to compute.
The conversion consists of three stages:
1. sRGB to Linear sRGB
2. Linear sRGB to OKLab
3. OKLab to OKLCH.
For references of colors in the OKLCH space, and how they correspond to sRGB colors, please see <https://OKLCH.com/>.
**Syntax**
```
colorSRGBToOKLCH(tuple[, gamma])
```
**Arguments**
- `tuple` β Tuple of three values R, G, B in the range `[0...255]`. [`Tuple(UInt8, UInt8, UInt8)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
- `gamma` β Optional. Exponent that is used to linearize sRGB by applying `(x / 255)^gamma` to each channel `x`. Defaults to `2.2`. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a tuple (L, C, H) representing the OKLCH color space values. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Convert sRGB to OKLCH**
```
SELECT colorSRGBToOKLCH((128, 64, 32), 2.2) AS lch;
```
```
ββlchββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β (0.4436238384931984,0.1044269954567863,45.90734548193018) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## connectionId[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#connectionId "Direct link to connectionId")
Introduced in: v21.3.0
Returns the connection ID of the client that submitted the current query. This function is most useful in debugging scenarios. It was created for compatibility with MySQL's `CONNECTION_ID` function. It is not typically used in production queries.
**Syntax**
```
connectionId()
```
**Arguments**
- None.
**Returned value**
Returns the connection ID of the current client. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT connectionId();
```
```
ββconnectionId()ββ
β 0 β
ββββββββββββββββββ
```
## countDigits[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#countDigits "Direct link to countDigits")
Introduced in: v20.8.0
Returns the number of decimal digits needed to represent a value.
Note
This function takes into account the scales of decimal values i.e., it calculates the result over the underlying integer type which is `(value * scale)`.
For example:
- `countDigits(42) = 2`
- `countDigits(42.000) = 5`
- `countDigits(0.04200) = 4`
Tip
You can check decimal overflow for `Decimal64` with `countDigits(x) > 18`, although it is slower than [`isDecimalOverflow`](https://clickhouse.com/docs/sql-reference/functions/other-functions#isDecimalOverflow).
**Syntax**
```
countDigits(x)
```
**Arguments**
- `x` β An integer or decimal value. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns the number of digits needed to represent `x`. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT countDigits(toDecimal32(1, 9)), countDigits(toDecimal32(-1, 9)),
countDigits(toDecimal64(1, 18)), countDigits(toDecimal64(-1, 18)),
countDigits(toDecimal128(1, 38)), countDigits(toDecimal128(-1, 38));
```
```
ββcountDigits(toDecimal32(1, 9))ββ¬βcountDigits(toDecimal32(-1, 9))ββ¬βcountDigits(toDecimal64(1, 18))ββ¬βcountDigits(toDecimal64(-1, 18))ββ¬βcountDigits(toDecimal128(1, 38))ββ¬βcountDigits(toDecimal128(-1, 38))ββ
β 10 β 10 β 19 β 19 β 39 β 39 β
ββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββ
```
## currentDatabase[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentDatabase "Direct link to currentDatabase")
Introduced in: v1.1.0
Returns the name of the current database. Useful in table engine parameters of `CREATE TABLE` queries where you need to specify the database.
Also see the [`SET` statement](https://clickhouse.com/docs/sql-reference/statements/use).
**Syntax**
```
currentDatabase()
```
**Aliases**: `current_database`, `SCHEMA`, `DATABASE`
**Arguments**
- None.
**Returned value**
Returns the current database name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT currentDatabase()
```
```
ββcurrentDatabase()ββ
β default β
βββββββββββββββββββββ
```
**SQL standard syntax without parentheses**
```
SELECT CURRENT_DATABASE
```
```
ββCURRENT_DATABASEββ
β default β
ββββββββββββββββββββ
```
## currentProfiles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentProfiles "Direct link to currentProfiles")
Introduced in: v21.9.0
Returns an array of the setting profiles for the current user.
**Syntax**
```
currentProfiles()
```
**Arguments**
- None.
**Returned value**
Returns an array of setting profiles for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT currentProfiles();
```
```
ββcurrentProfiles()ββββββββββββββββββββββββββββββ
β ['default', 'readonly_user', 'web_analytics'] β
βββββββββββββββββββββββββββββββββββββββββββββββββ
```
## currentQueryID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentQueryID "Direct link to currentQueryID")
Introduced in: v25.2.0
Returns current Query id.
**Syntax**
```
currentQueryID()
```
**Aliases**: `current_query_id`
**Arguments**
- None.
**Returned value**
**Examples**
**Example**
```
SELECT currentQueryID();
```
```
ββcurrentQueryID()ββββββββββββββββββββββ
β 1280d0e8-1a08-4524-be6e-77975bb68e7d β
ββββββββββββββββββββββββββββββββββββββββ
```
## currentRoles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentRoles "Direct link to currentRoles")
Introduced in: v21.9.0
Returns an array of the roles which are assigned to the current user.
**Syntax**
```
currentRoles()
```
**Arguments**
- None.
**Returned value**
Returns an array of the roles which are assigned to the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT currentRoles();
```
```
ββcurrentRoles()ββββββββββββββββββββββββββββββββββ
β ['sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## currentSchemas[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentSchemas "Direct link to currentSchemas")
Introduced in: v23.7.0
Same as function [`currentDatabase`](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentDatabase) but
- accepts a boolean argument which is ignored
- returns the database name as an array with a single value.
Function `currentSchemas` only exists for compatibility with PostgreSQL. Please use `currentDatabase` instead.
Also see the [`SET` statement](https://clickhouse.com/docs/sql-reference/statements/use).
**Syntax**
```
currentSchemas(bool)
```
**Aliases**: `current_schemas`
**Arguments**
- `bool` β A boolean value, which is ignored. [`Bool`](https://clickhouse.com/docs/sql-reference/data-types/boolean)
**Returned value**
Returns a single-element array with the name of the current database. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT currentSchemas(true)
```
```
ββcurrentSchemas(true)ββ
β ['default'] β
ββββββββββββββββββββββββ
```
## currentUser[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#currentUser "Direct link to currentUser")
Introduced in: v20.1.0
Returns the name of the current user. In case of a distributed query, the name of the user who initiated the query is returned.
**Syntax**
```
currentUser()
```
**Aliases**: `current_user`, `user`
**Arguments**
- None.
**Returned value**
Returns the name of the current user, otherwise the login of the user who initiated the query. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT currentUser()
```
```
ββcurrentUser()ββ
β default β
βββββββββββββββββ
```
**SQL standard syntax without parentheses**
```
SELECT CURRENT_USER
```
```
ββCURRENT_USERββ
β default β
ββββββββββββββββ
```
## defaultProfiles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultProfiles "Direct link to defaultProfiles")
Introduced in: v21.9.0
Returns an array of default setting profile names for the current user.
**Syntax**
```
defaultProfiles()
```
**Arguments**
- None.
**Returned value**
Returns an array of default setting profile names for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT defaultProfiles();
```
```
ββdefaultProfiles()ββ
β ['default'] β
βββββββββββββββββββββ
```
## defaultRoles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultRoles "Direct link to defaultRoles")
Introduced in: v21.9.0
Returns an array of default roles for the current user.
**Syntax**
```
defaultRoles()
```
**Arguments**
- None.
**Returned value**
Returns an array of default roles for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT defaultRoles();
```
```
ββdefaultRoles()ββββββββββββββββββββββββββββββββββ
β ['sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## defaultValueOfArgumentType[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultValueOfArgumentType "Direct link to defaultValueOfArgumentType")
Introduced in: v1.1.0
Returns the default value for a given data type. Does not include default values for custom columns set by the user.
**Syntax**
```
defaultValueOfArgumentType(expression)
```
**Arguments**
- `expression` β Arbitrary type of value or an expression that results in a value of an arbitrary type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns `0` for numbers, an empty string for strings or `NULL` for Nullable types. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`NULL`](https://clickhouse.com/docs/sql-reference/syntax#null)
**Examples**
**Usage example**
```
SELECT defaultValueOfArgumentType(CAST(1 AS Int8));
```
```
ββdefaultValueOfArgumentType(CAST(1, 'Int8'))ββ
β 0 β
βββββββββββββββββββββββββββββββββββββββββββββββ
```
**Nullable example**
```
SELECT defaultValueOfArgumentType(CAST(1 AS Nullable(Int8)));
```
```
ββdefaultValueOfArgumentType(CAST(1, 'Nullable(Int8)'))ββ
β α΄Ία΅α΄Έα΄Έ β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## defaultValueOfTypeName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#defaultValueOfTypeName "Direct link to defaultValueOfTypeName")
Introduced in: v1.1.0
Returns the default value for the given type name.
**Syntax**
```
defaultValueOfTypeName(type)
```
**Arguments**
- `type` β A string representing a type name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the default value for the given type name: `0` for numbers, an empty string for strings, or `NULL` for Nullable [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`NULL`](https://clickhouse.com/docs/sql-reference/syntax#null)
**Examples**
**Usage example**
```
SELECT defaultValueOfTypeName('Int8');
```
```
ββdefaultValueOfTypeName('Int8')ββ
β 0 β
ββββββββββββββββββββββββββββββββββ
```
**Nullable example**
```
SELECT defaultValueOfTypeName('Nullable(Int8)');
```
```
ββdefaultValueOfTypeName('Nullable(Int8)')ββ
β α΄Ία΅α΄Έα΄Έ β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## displayName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#displayName "Direct link to displayName")
Introduced in: v22.11.0
Returns the value of `display_name` from [config](https://clickhouse.com/docs/operations/configuration-files) or the server's Fully Qualified Domain Name (FQDN) if not set.
**Syntax**
```
displayName()
```
**Arguments**
- None.
**Returned value**
Returns the value of `display_name` from config or server FQDN if not set. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT displayName();
```
```
ββdisplayName()ββ
β production β
βββββββββββββββββ
```
## dumpColumnStructure[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#dumpColumnStructure "Direct link to dumpColumnStructure")
Introduced in: v1.1.0
Outputs a detailed description of the internal structure of a column and its data type.
**Syntax**
```
dumpColumnStructure(x)
```
**Arguments**
- `x` β Value for which to get the description of. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a description of the column structure used for representing the value. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT dumpColumnStructure(CAST('2018-01-01 01:02:03', 'DateTime'));
```
```
ββdumpColumnStructure(CAST('2018-01-01 01:02:03', 'DateTime'))ββ
β DateTime, Const(size = 1, UInt32(size = 1)) β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## enabledProfiles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#enabledProfiles "Direct link to enabledProfiles")
Introduced in: v21.9.0
Returns an array of setting profile names which are enabled for the current user.
**Syntax**
```
enabledProfiles()
```
**Arguments**
- None.
**Returned value**
Returns an array of setting profile names which are enabled for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT enabledProfiles();
```
```
ββenabledProfiles()ββββββββββββββββββββββββββββββββββββββββββββββββββ
β ['default', 'readonly_user', 'web_analytics', 'batch_processing'] β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## enabledRoles[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#enabledRoles "Direct link to enabledRoles")
Introduced in: v21.9.0
Returns an array of the roles which are enabled for the current user.
**Syntax**
```
enabledRoles()
```
**Arguments**
- None.
**Returned value**
Returns an array of role names which are enabled for the current user. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**Usage example**
```
SELECT enabledRoles();
```
```
ββenabledRoles()ββββββββββββββββββββββββββββββββββββββββββββββββββ
β ['general_data', 'sql-console-role:jane.smith@clickhouse.com'] β
ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## errorCodeToName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#errorCodeToName "Direct link to errorCodeToName")
Introduced in: v20.12.0
Returns the textual name of a numeric ClickHouse error code. The mapping from numeric error codes to error names is available [here](https://github.com/ClickHouse/ClickHouse/blob/master/src/Common/ErrorCodes.cpp).
**Syntax**
```
errorCodeToName(error_code)
```
**Arguments**
- `error_code` β ClickHouse error code. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns the textual name of `error_code`. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT errorCodeToName(252);
```
```
ββerrorCodeToName(252)ββ
β TOO_MANY_PARTS β
ββββββββββββββββββββββββ
```
## file[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#file "Direct link to file")
Introduced in: v21.3.0
Reads a file as a string and loads the data into the specified column. The file content is not interpreted.
Also see the [`file`](https://clickhouse.com/docs/sql-reference/table-functions/file) table function.
**Syntax**
```
file(path[, default])
```
**Arguments**
- `path` β The path of the file relative to the `user_files_path`. Supports wildcards `*`, `**`, `?`, `{abc,def}` and `{N..M}` where `N`, `M` are numbers and `'abc', 'def'` are strings. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `default` β The value returned if the file does not exist or cannot be accessed. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`NULL`](https://clickhouse.com/docs/sql-reference/syntax#null)
**Returned value**
Returns the file content as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Insert files into a table**
```
INSERT INTO table SELECT file('a.txt'), file('b.txt');
```
## filesystemAvailable[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemAvailable "Direct link to filesystemAvailable")
Introduced in: v20.1.0
Returns the amount of free space in the filesystem hosting the database persistence. The returned value is always smaller than the total free space ([`filesystemUnreserved`](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemUnreserved)) because some space is reserved for the operating system.
**Syntax**
```
filesystemAvailable([disk_name])
```
**Arguments**
- `disk_name` β Optional. The disk name to find the amount of free space for. If omitted, uses the default disk. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring)
**Returned value**
Returns the amount of remaining space available in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT formatReadableSize(filesystemAvailable()) AS "Available space";
```
```
ββAvailable spaceββ
β 30.75 GiB β
βββββββββββββββββββ
```
## filesystemCapacity[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemCapacity "Direct link to filesystemCapacity")
Introduced in: v20.1.0
Returns the capacity of the filesystem in bytes. Needs the [path](https://clickhouse.com/docs/operations/server-configuration-parameters/settings#path) to the data directory to be configured.
**Syntax**
```
filesystemCapacity([disk_name])
```
**Arguments**
- `disk_name` β Optional. The disk name to get the capacity for. If omitted, uses the default disk. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring)
**Returned value**
Returns the capacity of the filesystem in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT formatReadableSize(filesystemCapacity()) AS "Capacity";
```
```
ββCapacityβββ
β 39.32 GiB β
βββββββββββββ
```
## filesystemUnreserved[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemUnreserved "Direct link to filesystemUnreserved")
Introduced in: v22.12.0
Returns the total amount of free space on the filesystem hosting the database persistence (previously `filesystemFree`). See also [`filesystemAvailable`](https://clickhouse.com/docs/sql-reference/functions/other-functions#filesystemAvailable).
**Syntax**
```
filesystemUnreserved([disk_name])
```
**Arguments**
- `disk_name` β Optional. The disk name for which to find the total amount of free space. If omitted, uses the default disk. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring)
**Returned value**
Returns the amount of free space in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT formatReadableSize(filesystemUnreserved()) AS "Free space";
```
```
ββFree spaceββ
β 32.39 GiB β
ββββββββββββββ
```
## finalizeAggregation[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#finalizeAggregation "Direct link to finalizeAggregation")
Introduced in: v1.1.0
Given an aggregation state, this function returns the result of aggregation (or the finalized state when using a [\-State](https://clickhouse.com/docs/sql-reference/aggregate-functions/combinators#-state) combinator).
**Syntax**
```
finalizeAggregation(state)
```
**Arguments**
- `state` β State of aggregation. [`AggregateFunction`](https://clickhouse.com/docs/sql-reference/data-types/aggregatefunction)
**Returned value**
Returns the finalized result of aggregation. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(arrayReduce('maxState', [1, 2, 3]));
```
```
ββfinalizeAggregation(arrayReduce('maxState', [1, 2, 3]))ββ
β 3 β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
**Combined with initializeAggregation**
```
WITH initializeAggregation('sumState', number) AS one_row_sum_state
SELECT
number,
finalizeAggregation(one_row_sum_state) AS one_row_sum,
runningAccumulate(one_row_sum_state) AS cumulative_sum
FROM numbers(5);
```
```
ββnumberββ¬βone_row_sumββ¬βcumulative_sumββ
β 0 β 0 β 0 β
β 1 β 1 β 1 β
β 2 β 2 β 3 β
β 3 β 3 β 6 β
β 4 β 4 β 10 β
ββββββββββ΄ββββββββββββββ΄βββββββββββββββββ
```
## flipCoordinates[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#flipCoordinates "Direct link to flipCoordinates")
Introduced in: v25.10.0
Flips the x and y coordinates of geometric objects. This operation swaps latitude and longitude, which is useful for converting between different coordinate systems or correcting coordinate order.
For a Point, it swaps the x and y coordinates. For complex geometries (LineString, Polygon, MultiPolygon, Ring, MultiLineString), it recursively applies the transformation to each coordinate pair.
The function supports both individual geometry types (Point, Ring, Polygon, MultiPolygon, LineString, MultiLineString) and the Geometry variant type.
**Syntax**
```
flipCoordinates(geometry)
```
**Arguments**
- `geometry` β The geometry to transform. Supported types: Point (Tuple(Float64, Float64)), Ring (Array(Point)), Polygon (Array(Ring)), MultiPolygon (Array(Polygon)), LineString (Array(Point)), MultiLineString (Array(LineString)), or Geometry (a variant containing any of these types).
**Returned value**
The geometry with flipped coordinates. The return type matches the input type. [`Point`](https://clickhouse.com/docs/sql-reference/data-types/geo#point) or [`Ring`](https://clickhouse.com/docs/sql-reference/data-types/geo#ring) or [`Polygon`](https://clickhouse.com/docs/sql-reference/data-types/geo#polygon) or [`MultiPolygon`](https://clickhouse.com/docs/sql-reference/data-types/geo#multipolygon) or [`LineString`](https://clickhouse.com/docs/sql-reference/data-types/geo#linestring) or [`MultiLineString`](https://clickhouse.com/docs/sql-reference/data-types/geo#multilinestring) or [`Geometry`](https://clickhouse.com/docs/sql-reference/data-types/geo)
**Examples**
**basic\_point**
```
SELECT flipCoordinates((1.0, 2.0));
```
```
(2.0, 1.0)
```
**ring**
```
SELECT flipCoordinates([(1.0, 2.0), (3.0, 4.0)]);
```
```
[(2.0, 1.0), (4.0, 3.0)]
```
**polygon**
```
SELECT flipCoordinates([[(1.0, 2.0), (3.0, 4.0)], [(5.0, 6.0), (7.0, 8.0)]]);
```
```
[[(2.0, 1.0), (4.0, 3.0)], [(6.0, 5.0), (8.0, 7.0)]]
```
**geometry\_wkt**
```
SELECT flipCoordinates(readWkt('POINT(10 20)'));
```
```
(20, 10)
```
**geometry\_polygon\_wkt**
```
SELECT flipCoordinates(readWkt('POLYGON((0 0, 5 0, 5 5, 0 5, 0 0))'));
```
```
[[(0, 0), (0, 5), (5, 5), (5, 0), (0, 0)]]
```
## formatQuery[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuery "Direct link to formatQuery")
Introduced in: v23.10.0
Returns a formatted, possibly multi-line, version of the given SQL query. Throws in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQuery(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuery('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT
a,
b
FROM tab
WHERE (a > 3) AND (b < 3)
```
## formatQueryOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQueryOrNull "Direct link to formatQueryOrNull")
Introduced in: v23.11.0
Returns a formatted, possibly multi-line, version of the given SQL query. Returns NULL in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQueryOrNull(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuery('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT
a,
b
FROM tab
WHERE (a > 3) AND (b < 3)
```
## formatQuerySingleLine[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuerySingleLine "Direct link to formatQuerySingleLine")
Introduced in: v23.10.0
Like formatQuery() but the returned formatted string contains no line breaks. Throws in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQuerySingleLine(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuerySingleLine('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT a, b FROM tab WHERE (a > 3) AND (b < 3)
```
## formatQuerySingleLineOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatQuerySingleLineOrNull "Direct link to formatQuerySingleLineOrNull")
Introduced in: v23.11.0
Like formatQuery() but the returned formatted string contains no line breaks. Returns NULL in case of a parsing error. \[example:multiline\]
**Syntax**
```
formatQuerySingleLineOrNull(query)
```
**Arguments**
- `query` β The SQL query to be formatted. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The formatted query [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**multiline**
```
SELECT formatQuerySingleLine('select a, b FRom tab WHERE a > 3 and b < 3');
```
```
SELECT a, b FROM tab WHERE (a > 3) AND (b < 3)
```
## formatReadableDecimalSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize "Direct link to formatReadableDecimalSize")
Introduced in: v22.11.0
Given a size (number of bytes), this function returns a readable, rounded size with suffix (KB, MB, etc.) as a string.
The opposite operations of this function are [`parseReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize).
**Syntax**
```
formatReadableDecimalSize(x)
```
**Arguments**
- `x` β Size in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a readable, rounded size with suffix as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Format file sizes**
```
SELECT
arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
formatReadableDecimalSize(filesize_bytes) AS filesize
```
```
ββfilesize_bytesββ¬βfilesizeββββ
β 1 β 1.00 B β
β 1024 β 1.02 KB β
β 1048576 β 1.05 MB β
β 192851925 β 192.85 MB β
ββββββββββββββββββ΄βββββββββββββ
```
## formatReadableQuantity[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableQuantity "Direct link to formatReadableQuantity")
Introduced in: v20.10.0
Given a number, this function returns a rounded number with suffix (thousand, million, billion, etc.) as a string.
This function accepts any numeric type as input, but internally it casts them to `Float64`. Results might be suboptimal with large values.
**Syntax**
```
formatReadableQuantity(x)
```
**Arguments**
- `x` β A number to format. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a rounded number with suffix as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Format numbers with suffixes**
```
SELECT
arrayJoin([1024, 1234 * 1000, (4567 * 1000) * 1000, 98765432101234]) AS number,
formatReadableQuantity(number) AS number_for_humans
```
```
ββββββββββnumberββ¬βnumber_for_humansββ
β 1024 β 1.02 thousand β
β 1234000 β 1.23 million β
β 4567000000 β 4.57 billion β
β 98765432101234 β 98.77 trillion β
ββββββββββββββββββ΄ββββββββββββββββββββ
```
## formatReadableSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize "Direct link to formatReadableSize")
Introduced in: v1.1.0
Given a size (number of bytes), this function returns a readable, rounded size with suffix (KiB, MiB, etc.) as string.
The opposite operations of this function are [`parseReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize), [`parseReadableSizeOrZero`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrZero), and [`parseReadableSizeOrNull`](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrNull). This function accepts any numeric type as input, but internally it casts them to `Float64`. Results might be suboptimal with large values.
**Syntax**
```
formatReadableSize(x)
```
**Aliases**: `FORMAT_BYTES`
**Arguments**
- `x` β Size in bytes. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns a readable, rounded size with suffix as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Format file sizes**
```
SELECT
arrayJoin([1, 1024, 1024*1024, 192851925]) AS filesize_bytes,
formatReadableSize(filesize_bytes) AS filesize
```
```
ββfilesize_bytesββ¬βfilesizeββββ
β 1 β 1.00 B β
β 1024 β 1.00 KiB β
β 1048576 β 1.00 MiB β
β 192851925 β 183.92 MiB β
ββββββββββββββββββ΄βββββββββββββ
```
## formatReadableTimeDelta[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableTimeDelta "Direct link to formatReadableTimeDelta")
Introduced in: v20.12.0
Given a time interval (delta) in seconds, this function returns a time delta with year/month/day/hour/minute/second/millisecond/microsecond/nanosecond as a string.
This function accepts any numeric type as input, but internally it casts them to `Float64`. Results might be suboptimal with large values.
**Syntax**
```
formatReadableTimeDelta(column[, maximum_unit, minimum_unit])
```
**Arguments**
- `column` β A column with a numeric time delta. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `maximum_unit` β Optional. Maximum unit to show. Acceptable values: `nanoseconds`, `microseconds`, `milliseconds`, `seconds`, `minutes`, `hours`, `days`, `months`, `years`. Default value: `years`. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `minimum_unit` β Optional. Minimum unit to show. All smaller units are truncated. Acceptable values: `nanoseconds`, `microseconds`, `milliseconds`, `seconds`, `minutes`, `hours`, `days`, `months`, `years`. If explicitly specified value is bigger than `maximum_unit`, an exception will be thrown. Default value: `seconds` if `maximum_unit` is `seconds` or bigger, `nanoseconds` otherwise. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a time delta as a string. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT
arrayJoin([100, 12345, 432546534]) AS elapsed,
formatReadableTimeDelta(elapsed) AS time_delta
```
```
βββββelapsedββ¬βtime_deltaββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β 100 β 1 minute and 40 seconds β
β 12345 β 3 hours, 25 minutes and 45 seconds β
β 432546534 β 13 years, 8 months, 17 days, 7 hours, 48 minutes and 54 secondsβ
ββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
**With maximum unit**
```
SELECT
arrayJoin([100, 12345, 432546534]) AS elapsed,
formatReadableTimeDelta(elapsed, 'minutes') AS time_delta
```
```
βββββelapsedββ¬βtime_deltaββββββββββββββββββββββββββββββββββββββββββββββββββββββ
β 100 β 1 minute and 40 seconds β
β 12345 β 205 minutes and 45 seconds β
β 432546534 β 7209108 minutes and 54 seconds β
ββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## fuzzQuery[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#fuzzQuery "Direct link to fuzzQuery")
Introduced in: v26.2.0
Parses the given query string and applies random AST mutations (fuzzing) to it. Returns the fuzzed query as a string. Non-deterministic: each call may produce a different result. Requires `allow_fuzz_query_functions = 1`.
**Syntax**
```
fuzzQuery(query)
```
**Arguments**
- `query` β The SQL query to be fuzzed. [String](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The fuzzed query string [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**basic**
```
SET allow_fuzz_query_functions = 1; SELECT fuzzQuery('SELECT 1');
```
## generateRandomStructure[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#generateRandomStructure "Direct link to generateRandomStructure")
Introduced in: v23.5.0
Generates random table structure in the format `column1_name column1_type, column2_name column2_type, ...`.
**Syntax**
```
generateRandomStructure([number_of_columns, seed])
```
**Arguments**
- `number_of_columns` β The desired number of columns in the resultant table structure. If set to 0 or `Null`, the number of columns will be random from 1 to 128. Default value: `Null`. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
- `seed` β Random seed to produce stable results. If seed is not specified or set to `Null`, it is randomly generated. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Randomly generated table structure. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT generateRandomStructure()
```
```
c1 Decimal32(5), c2 Date, c3 Tuple(LowCardinality(String), Int128, UInt64, UInt16, UInt8, IPv6), c4 Array(UInt128), c5 UInt32, c6 IPv4, c7 Decimal256(64), c8 Decimal128(3), c9 UInt256, c10 UInt64, c11 DateTime
```
**with specified number of columns**
```
SELECT generateRandomStructure(1)
```
```
c1 Map(UInt256, UInt16)
```
**with specified seed**
```
SELECT generateRandomStructure(NULL, 33)
```
```
c1 DateTime, c2 Enum8('c2V0' = 0, 'c2V1' = 1, 'c2V2' = 2, 'c2V3' = 3), c3 LowCardinality(Nullable(FixedString(30))), c4 Int16, c5 Enum8('c5V0' = 0, 'c5V1' = 1, 'c5V2' = 2, 'c5V3' = 3), c6 Nullable(UInt8), c7 String, c8 Nested(e1 IPv4, e2 UInt8, e3 UInt16, e4 UInt16, e5 Int32, e6 Map(Date, Decimal256(70)))
```
## generateSerialID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#generateSerialID "Direct link to generateSerialID")
Introduced in: v25.1.0
Generates and returns sequential numbers starting from the previous counter value. This function takes a string argument - a series identifier, and an optional starting value. The server should be configured with Keeper. The series are stored in Keeper nodes under the path, which can be configured in [`series_keeper_path`](https://clickhouse.com/docs/operations/server-configuration-parameters/settings#series_keeper_path) in the server configuration.
**Syntax**
```
generateSerialID(series_identifier[, start_value])
```
**Arguments**
- `series_identifier` β Series identifier [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `start_value` β Optional. Starting value for the counter. Defaults to 0. Note: this value is only used when creating a new series and is ignored if the series already exists [`UInt*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns sequential numbers starting from the previous counter value. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**first call**
```
SELECT generateSerialID('id1')
```
```
ββgenerateSerialID('id1')βββ
β 1 β
ββββββββββββββββββββββββββββ
```
**second call**
```
SELECT generateSerialID('id1')
```
```
ββgenerateSerialID('id1')βββ
β 2 β
ββββββββββββββββββββββββββββ
```
**column call**
```
SELECT *, generateSerialID('id1') FROM test_table
```
```
ββCounterIDββ¬βUserIDββ¬βverββ¬βgenerateSerialID('id1')βββ
β 1 β 3 β 3 β 3 β
β 1 β 1 β 1 β 4 β
β 1 β 2 β 2 β 5 β
β 1 β 5 β 5 β 6 β
β 1 β 4 β 4 β 7 β
βββββββββββββ΄βββββββββ΄ββββββ΄βββββββββββββββββββββββββββ
```
**with start value**
```
SELECT generateSerialID('id2', 100)
```
```
ββgenerateSerialID('id2', 100)βββ
β 100 β
βββββββββββββββββββββββββββββββββ
```
**with start value second call**
```
SELECT generateSerialID('id2', 100)
```
```
ββgenerateSerialID('id2', 100)βββ
β 101 β
βββββββββββββββββββββββββββββββββ
```
Introduced in: v24.5.0
Gets the value of an HTTP header. If there is no such header or the current request is not performed via the HTTP interface, the function returns an empty string. Certain HTTP headers (e.g., `Authentication` and `X-ClickHouse-*`) are restricted.
Note
Setting `allow_get_client_http_header` is required
The function requires the setting `allow_get_client_http_header` to be enabled. The setting is not enabled by default for security reasons, because some headers, such as `Cookie`, could contain sensitive info.
HTTP headers are case sensitive for this function. If the function is used in the context of a distributed query, it returns non-empty result only on the initiator node.
**Syntax**
```
getClientHTTPHeader(name)
```
**Arguments**
- `name` β The HTTP header name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the value of the header. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT getClientHTTPHeader('Content-Type');
```
```
ββgetClientHTTPHeader('Content-Type')ββ
β application/x-www-form-urlencoded β
βββββββββββββββββββββββββββββββββββββββ
```
## getMacro[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMacro "Direct link to getMacro")
Introduced in: v20.1.0
Returns the value of a macro from the server configuration file. Macros are defined in the [`<macros>`](https://clickhouse.com/docs/operations/server-configuration-parameters/settings#macros) section of the configuration file and can be used to distinguish servers by convenient names even if they have complicated hostnames. If the function is executed in the context of a distributed table, it generates a normal column with values relevant to each shard.
**Syntax**
```
getMacro(name)
```
**Arguments**
- `name` β The name of the macro to retrieve. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the value of the specified macro. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Basic usage**
```
SELECT getMacro('test');
```
```
ββgetMacro('test')ββ
β Value β
ββββββββββββββββββββ
```
## getMaxTableNameLengthForDatabase[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMaxTableNameLengthForDatabase "Direct link to getMaxTableNameLengthForDatabase")
Introduced in: v25.1.0
Returns the maximum table name length in a specified database.
**Syntax**
```
getMaxTableNameLengthForDatabase(database_name)
```
**Arguments**
- `database_name` β The name of the specified database. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the length of the maximum table name, an Integer
**Examples**
**typical**
```
SELECT getMaxTableNameLengthForDatabase('default');
```
```
ββgetMaxTableNameLengthForDatabase('default')ββ
β 206 β
βββββββββββββββββββββββββββββββββββββββββββββββ
```
## getMergeTreeSetting[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getMergeTreeSetting "Direct link to getMergeTreeSetting")
Introduced in: v25.6.0
Returns the current value of a MergeTree setting.
**Syntax**
```
getMergeTreeSetting(setting_name)
```
**Arguments**
- `setting_name` β The setting name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the merge tree setting's current value.
**Examples**
**Usage example**
```
SELECT getMergeTreeSetting('index_granularity');
```
```
ββgetMergeTreeSetting('index_granularity')ββ
β 8192 β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## getOSKernelVersion[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getOSKernelVersion "Direct link to getOSKernelVersion")
Introduced in: v21.11.0
Returns a string with the OS kernel version.
**Syntax**
```
getOSKernelVersion()
```
**Arguments**
- None.
**Returned value**
Returns the current OS kernel version. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT getOSKernelVersion();
```
```
ββgetOSKernelVersion()βββββ
β Linux 4.15.0-55-generic β
βββββββββββββββββββββββββββ
```
## getServerPort[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getServerPort "Direct link to getServerPort")
Introduced in: v21.10.0
Returns the server's port number for a given protocol.
**Syntax**
```
getServerPort(port_name)
```
**Arguments**
- `port_name` β The name of the port. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the server port number. [`UInt16`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT getServerPort('tcp_port');
```
```
ββgetServerPort('tcp_port')ββ
β 9000 β
βββββββββββββββββββββββββββββ
```
## getServerSetting[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getServerSetting "Direct link to getServerSetting")
Introduced in: v25.6.0
Returns the currently set value, given a server setting name.
**Syntax**
```
getServerSetting(setting_name')
```
**Arguments**
- `setting_name` β The server setting name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the server setting's current value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT getServerSetting('allow_use_jemalloc_memory');
```
```
ββgetServerSetting('allow_use_jemalloc_memory')ββ
β true β
βββββββββββββββββββββββββββββββββββββββββββββββββ
```
## getSetting[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSetting "Direct link to getSetting")
Introduced in: v20.7.0
Returns the current value of a setting.
**Syntax**
```
getSetting(setting_name)
```
**Arguments**
- `setting_Name` β The setting name. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the setting's current value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT getSetting('enable_analyzer');
SET enable_analyzer = false;
SELECT getSetting('enable_analyzer');
```
```
ββgetSetting('β―_analyzer')ββ
β true β
ββββββββββββββββββββββββββββ
ββgetSetting('β―_analyzer')ββ
β false β
ββββββββββββββββββββββββββββ
```
## getSettingOrDefault[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSettingOrDefault "Direct link to getSettingOrDefault")
Introduced in: v24.10.0
Returns the current value of a setting or returns the default value specified in the second argument if the setting is not set in the current profile.
**Syntax**
```
getSettingOrDefault(setting_name, default_value)
```
**Arguments**
- `setting_name` β The setting name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `default_value` β Value to return if custom\_setting is not set. Value may be of any data type or Null.
**Returned value**
Returns the current value of the specified setting or `default_value` if the setting is not set.
**Examples**
**Usage example**
```
SELECT getSettingOrDefault('custom_undef1', 'my_value');
SELECT getSettingOrDefault('custom_undef2', 100);
SELECT getSettingOrDefault('custom_undef3', NULL);
```
```
my_value
100
NULL
```
## getSizeOfEnumType[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSizeOfEnumType "Direct link to getSizeOfEnumType")
Introduced in: v1.1.0
Returns the number of fields in the given [`Enum`](https://clickhouse.com/docs/sql-reference/data-types/enum).
**Syntax**
```
getSizeOfEnumType(x)
```
**Arguments**
- `x` β Value of type `Enum`. [`Enum`](https://clickhouse.com/docs/sql-reference/data-types/enum)
**Returned value**
Returns the number of fields with `Enum` input values. [`UInt8/16`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT getSizeOfEnumType(CAST('a' AS Enum8('a' = 1, 'b' = 2))) AS x;
```
```
ββxββ
β 2 β
βββββ
```
## getSubcolumn[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getSubcolumn "Direct link to getSubcolumn")
Introduced in: v23.3.0
Receives the expression or identifier and constant string with the name of subcolumn.
Returns requested subcolumn extracted from the expression.
**Syntax**
```
getSubcolumn(nested_value, subcolumn_name)
```
**Arguments**
- None.
**Returned value**
**Examples**
**getSubcolumn**
```
SELECT getSubcolumn(array_col, 'size0'), getSubcolumn(tuple_col, 'elem_name')
```
## getTypeSerializationStreams[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#getTypeSerializationStreams "Direct link to getTypeSerializationStreams")
Introduced in: v22.6.0
Enumerates stream paths of a data type. This function is intended for developmental use.
**Syntax**
```
getTypeSerializationStreams(col)
```
**Arguments**
- `col` β Column or string representation of a data-type from which the data type will be detected. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns an array with all the serialization sub-stream paths. [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array)
**Examples**
**tuple**
```
SELECT getTypeSerializationStreams(tuple('a', 1, 'b', 2))
```
```
['{TupleElement(1), Regular}','{TupleElement(2), Regular}','{TupleElement(3), Regular}','{TupleElement(4), Regular}']
```
**map**
```
SELECT getTypeSerializationStreams('Map(String, Int64)')
```
```
['{ArraySizes}','{ArrayElements, TupleElement(keys), Regular}','{ArrayElements, TupleElement(values), Regular}']
```
## globalVariable[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#globalVariable "Direct link to globalVariable")
Introduced in: v20.5.0
Takes a constant string argument and returns the value of the global variable with that name. This function is intended for compatibility with MySQL and not needed or useful for normal operation of ClickHouse. Only few dummy global variables are defined.
**Syntax**
```
globalVariable(name)
```
**Arguments**
- `name` β Global variable name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the value of variable `name`. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**globalVariable**
```
SELECT globalVariable('max_allowed_packet')
```
```
67108864
```
## hasColumnInTable[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#hasColumnInTable "Direct link to hasColumnInTable")
Introduced in: v1.1.0
Checks if a specific column exists in a database table. For elements in a nested data structure, the function checks for the existence of a column. For the nested data structure itself, the function returns `0`.
**Syntax**
```
hasColumnInTable([hostname[, username[, password]],]database, table, column)
```
**Arguments**
- `database` β Name of the database. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `table` β Name of the table. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `column` β Name of the column. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `hostname` β Optional. Remote server name to perform the check on. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `username` β Optional. Username for remote server. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `password` β Optional. Password for remote server. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns `1` if the given column exists, `0` otherwise. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Check an existing column**
```
SELECT hasColumnInTable('system','metrics','metric')
```
```
1
```
**Check a non-existing column**
```
SELECT hasColumnInTable('system','metrics','non-existing_column')
```
```
0
```
## hasThreadFuzzer[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#hasThreadFuzzer "Direct link to hasThreadFuzzer")
Introduced in: v20.6.0
Returns whether the thread fuzzer is enabled. THis function is only useful for testing and debugging.
**Syntax**
```
hasThreadFuzzer()
```
**Arguments**
- None.
**Returned value**
Returns whether Thread Fuzzer is effective. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Check Thread Fuzzer status**
```
SELECT hasThreadFuzzer()
```
```
ββhasThreadFuzzer()ββ
β 0 β
βββββββββββββββββββββ
```
## hostName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#hostName "Direct link to hostName")
Introduced in: v20.5.0
Returns the name of the host on which this function was executed. If the function executes on a remote server (distributed processing), the remote server name is returned. If the function executes in the context of a distributed table, it generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
hostName()
```
**Aliases**: `hostname`
**Arguments**
- None.
**Returned value**
Returns the host name. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT hostName()
```
```
ββhostName()ββ
β clickhouse β
ββββββββββββββ
```
## icebergBucket[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#icebergBucket "Direct link to icebergBucket")
Introduced in: v25.5.0
Implements logic for the [iceberg bucket transform](https://iceberg.apache.org/spec/#bucket-transform-details.)
**Syntax**
```
icebergBucket(N, value)
```
**Arguments**
- `N` β The number of buckets, modulo. [`const (U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
- `value` β The source value to transform. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Bool`](https://clickhouse.com/docs/sql-reference/data-types/boolean) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`FixedString`](https://clickhouse.com/docs/sql-reference/data-types/fixedstring) or [`UUID`](https://clickhouse.com/docs/sql-reference/data-types/uuid) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`Time`](https://clickhouse.com/docs/sql-reference/data-types/time) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
**Returned value**
Returns a 32-bit hash of the source value. [`Int32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Example**
```
SELECT icebergBucket(5, 1.0 :: Float32)
```
```
4
```
## icebergTruncate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#icebergTruncate "Direct link to icebergTruncate")
Introduced in: v25.3.0
Implements logic of iceberg truncate transform: <https://iceberg.apache.org/spec/#truncate-transform-details>.
**Syntax**
```
icebergTruncate(N, value)
```
**Arguments**
- `value` β The value to transform. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
The same type as the argument
**Examples**
**Example**
```
SELECT icebergTruncate(3, 'iceberg')
```
```
ice
```
## identity[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#identity "Direct link to identity")
Introduced in: v1.1.0
This function returns the argument you pass to it, which is useful for debugging and testing. It lets you bypass index usage to see full scan performance instead. The query analyzer ignores anything inside identity functions when looking for indexes to use, and it also disables constant folding.
**Syntax**
```
identity(x)
```
**Arguments**
- `x` β Input value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the input value unchanged. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT identity(42)
```
```
42
```
## ignore[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#ignore "Direct link to ignore")
Introduced in: v1.1.0
Accepts arbitrary arguments and unconditionally returns `0`.
**Syntax**
```
ignore(x)
```
**Arguments**
- `x` β An input value which is unused and passed only so as to avoid a syntax error. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Always returns `0`. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT ignore(0, 'ClickHouse', NULL)
```
```
ββignore(0, 'ClickHouse', NULL)ββ
β 0 β
βββββββββββββββββββββββββββββββββ
```
## indexHint[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#indexHint "Direct link to indexHint")
Introduced in: v1.1.0
This function is intended for debugging and introspection. It ignores its argument and always returns 1. The arguments are not evaluated.
During index analysis, the argument of this function is assumed to not be wrapped in `indexHint`. This allows you to select data in index ranges by the corresponding condition but without further filtering by this condition. The index in ClickHouse is sparse and using `indexHint` will yield more data than specifying the same condition directly.
Explanation
Note: It is not possible to optimize a query with the `indexHint` function. The `indexHint` function does not optimize the query, as it does not provide any additional information for the query analysis. Having an expression inside the `indexHint` function is not anyhow better than without the `indexHint` function. The `indexHint` function can be used only for introspection and debugging purposes and it does not improve performance. If you see the usage of `indexHint` by anyone other than ClickHouse contributors, it is likely a mistake and you should remove it.
**Syntax**
```
indexHint(expression)
```
**Arguments**
- `expression` β Any expression for index range selection. [`Expression`](https://clickhouse.com/docs/sql-reference/data-types/special-data-types/expression)
**Returned value**
Returns `1` in all cases. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example with date filtering**
```
SELECT FlightDate AS k, count() FROM ontime WHERE indexHint(k = '2025-09-15') GROUP BY k ORDER BY k ASC;
```
```
βββββββββββkββ¬βcount()ββ
β 2025-09-14 β 7071 β
β 2025-09-15 β 16428 β
β 2025-09-16 β 1077 β
β 2025-09-30 β 8167 β
ββββββββββββββ΄ββββββββββ
```
## initialQueryID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryID "Direct link to initialQueryID")
Introduced in: v1.1.0
Returns the ID of the initial current query. Other parameters of a query can be extracted from field `initial_query_id` in [`system.query_log`](https://clickhouse.com/docs/operations/system-tables/query_log).
In contrast to [`queryID`](https://clickhouse.com/docs/sql-reference/functions/other-functions#queryID) function, `initialQueryID` returns the same results on different shards.
**Syntax**
```
initialQueryID()
```
**Aliases**: `initial_query_id`
**Arguments**
- None.
**Returned value**
Returns the ID of the initial current query. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT initialQueryID() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
```
```
ββcount(DISTINCT t)ββ
β 1 β
βββββββββββββββββββββ
```
## initialQueryStartTime[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryStartTime "Direct link to initialQueryStartTime")
Introduced in: v25.4.0
Returns the start time of the initial current query. `initialQueryStartTime` returns the same results on different shards.
**Syntax**
```
initialQueryStartTime()
```
**Aliases**: `initial_query_start_time`
**Arguments**
- None.
**Returned value**
Returns the start time of the initial current query. [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
**Examples**
**Usage example**
```
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT initialQueryStartTime() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
```
```
ββcount(DISTINCT t)ββ
β 1 β
βββββββββββββββββββββ
```
## initializeAggregation[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#initializeAggregation "Direct link to initializeAggregation")
Introduced in: v20.6.0
Calculates the result of an aggregate function based on a single value. This function can be used to initialize aggregate functions with combinator [\-State](https://clickhouse.com/docs/sql-reference/aggregate-functions/combinators#-state). You can create states of aggregate functions and insert them to columns of type [`AggregateFunction`](https://clickhouse.com/docs/sql-reference/data-types/aggregatefunction) or use initialized aggregates as default values.
**Syntax**
```
initializeAggregation(aggregate_function, arg1[, arg2, ...])
```
**Arguments**
- `aggregate_function` β Name of the aggregation function to initialize. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `arg1[, arg2, ...]` β Arguments of the aggregate function. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the result of aggregation for every row passed to the function. The return type is the same as the return type of the function that `initializeAggregation` takes as a first argument. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Basic usage with uniqState**
```
SELECT uniqMerge(state) FROM (SELECT initializeAggregation('uniqState', number % 3) AS state FROM numbers(10000));
```
```
ββuniqMerge(state)ββ
β 3 β
ββββββββββββββββββββ
```
**Usage with sumState and finalizeAggregation**
```
SELECT finalizeAggregation(state), toTypeName(state) FROM (SELECT initializeAggregation('sumState', number % 3) AS state FROM numbers(5));
```
```
ββfinalizeAggregation(state)ββ¬βtoTypeName(state)ββββββββββββββ
β 0 β AggregateFunction(sum, UInt8) β
β 1 β AggregateFunction(sum, UInt8) β
β 2 β AggregateFunction(sum, UInt8) β
β 0 β AggregateFunction(sum, UInt8) β
β 1 β AggregateFunction(sum, UInt8) β
ββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββ
```
## isConstant[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#isConstant "Direct link to isConstant")
Introduced in: v20.3.0
Returns whether the argument is a constant expression. A constant expression is an expression whose result is known during query analysis, i.e. before execution. For example, expressions over [literals](https://clickhouse.com/docs/sql-reference/syntax#literals) are constant expressions. This function is mostly intended for development, debugging and demonstration.
**Syntax**
```
isConstant(x)
```
**Arguments**
- `x` β An expression to check. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns `1` if `x` is constant, `0` if `x` is non-constant. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Constant expression**
```
SELECT isConstant(x + 1)
FROM (SELECT 43 AS x)
```
```
ββisConstant(plus(x, 1))ββ
β 1 β
ββββββββββββββββββββββββββ
```
**Constant with function**
```
WITH 3.14 AS pi
SELECT isConstant(cos(pi))
```
```
ββisConstant(cos(pi))ββ
β 1 β
βββββββββββββββββββββββ
```
**Non-constant expression**
```
SELECT isConstant(number)
FROM numbers(1)
```
```
ββisConstant(number)ββ
β 0 β
ββββββββββββββββββββββ
```
**Behavior of the now() function**
```
SELECT isConstant(now())
```
```
ββisConstant(now())ββ
β 1 β
βββββββββββββββββββββ
```
## isDecimalOverflow[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#isDecimalOverflow "Direct link to isDecimalOverflow")
Introduced in: v20.8.0
Checks if a decimal number has too many digits to fit properly in a Decimal data type with given precision.
**Syntax**
```
isDecimalOverflow(value[, precision])
```
**Arguments**
- `value` β Decimal value to check. [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
- `precision` β Optional. The precision of the Decimal type. If omitted, the initial precision of the first argument is used. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns `1` if the decimal value has more digits than allowed by its precision, `0` if the decimal value satisfies the specified precision. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT isDecimalOverflow(toDecimal32(1000000000, 0), 9),
isDecimalOverflow(toDecimal32(1000000000, 0)),
isDecimalOverflow(toDecimal32(-1000000000, 0), 9),
isDecimalOverflow(toDecimal32(-1000000000, 0));
```
```
ββisDecimalOverflow(toDecimal32(1000000000, 0), 9)ββ¬βisDecimalOverflow(toDecimal32(1000000000, 0))ββ¬βisDecimalOverflow(toDecimal32(-1000000000, 0), 9)ββ¬βisDecimalOverflow(toDecimal32(-1000000000, 0))ββ
β 1 β 1 β 1 β 1 β
ββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββ
```
## joinGet[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGet "Direct link to joinGet")
Introduced in: v18.16.0
Allows you to extract data from a table the same way as from a dictionary. Gets data from Join tables using the specified join key.
Note
Only supports tables created with the `ENGINE = Join(ANY, LEFT, <join_keys>)` [statement](https://clickhouse.com/docs/engines/table-engines/special/join).
**Syntax**
```
joinGet(join_storage_table_name, value_column, join_keys)
```
**Arguments**
- `join_storage_table_name` β An identifier which indicates where to perform the search. The identifier is searched in the default database (see parameter `default_database` in the config file). To override the default database, use the `USE database_name` query or specify the database and the table through a dot, like `database_name.table_name`. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `value_column` β The name of the column of the table that contains required data. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `join_keys` β A list of join keys. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns list of values corresponded to list of keys. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13);
SELECT joinGet(db_test.id_val, 'val', toUInt32(1));
```
```
ββjoinGet(db_test.id_val, 'val', toUInt32(1))ββ
β 11 β
βββββββββββββββββββββββββββββββββββββββββββββββ
```
**Usage with table from current database**
```
USE db_test;
SELECT joinGet(id_val, 'val', toUInt32(2));
```
```
ββjoinGet(id_val, 'val', toUInt32(2))ββ
β 12 β
βββββββββββββββββββββββββββββββββββββββ
```
**Using arrays as join keys**
```
CREATE TABLE some_table (id1 UInt32, id2 UInt32, name String) ENGINE = Join(ANY, LEFT, id1, id2);
INSERT INTO some_table VALUES (1, 11, 'a') (2, 12, 'b') (3, 13, 'c');
SELECT joinGet(some_table, 'name', 1, 11);
```
```
ββjoinGet(some_table, 'name', 1, 11)ββ
β a β
ββββββββββββββββββββββββββββββββββββββ
```
## joinGetOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGetOrNull "Direct link to joinGetOrNull")
Introduced in: v20.4.0
Allows you to extract data from a table the same way as from a dictionary. Gets data from Join tables using the specified join key. Unlike [`joinGet`](https://clickhouse.com/docs/sql-reference/functions/other-functions#joinGet) it returns `NULL` when the key is missing.
Note
Only supports tables created with the `ENGINE = Join(ANY, LEFT, <join_keys>)` [statement](https://clickhouse.com/docs/engines/table-engines/special/join).
**Syntax**
```
joinGetOrNull(join_storage_table_name, value_column, join_keys)
```
**Arguments**
- `join_storage_table_name` β An identifier which indicates where to perform the search. The identifier is searched in the default database (see parameter default\_database in the config file). To override the default database, use the `USE database_name` query or specify the database and the table through a dot, like `database_name.table_name`. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `value_column` β The name of the column of the table that contains required data. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `join_keys` β A list of join keys. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a list of values corresponding to the list of keys, or `NULL` if a key is not found. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
CREATE TABLE db_test.id_val(`id` UInt32, `val` UInt32) ENGINE = Join(ANY, LEFT, id);
INSERT INTO db_test.id_val VALUES (1,11)(2,12)(4,13);
SELECT joinGetOrNull(db_test.id_val, 'val', toUInt32(1)), joinGetOrNull(db_test.id_val, 'val', toUInt32(999));
```
```
ββjoinGetOrNull(db_test.id_val, 'val', toUInt32(1))ββ¬βjoinGetOrNull(db_test.id_val, 'val', toUInt32(999))ββ
β 11 β α΄Ία΅α΄Έα΄Έ β
βββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## lowCardinalityIndices[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#lowCardinalityIndices "Direct link to lowCardinalityIndices")
Introduced in: v18.12.0
Returns the position of a value in the dictionary of a [LowCardinality](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality) column. Positions start at 1. Since LowCardinality have per-part dictionaries, this function may return different positions for the same value in different parts.
**Syntax**
```
lowCardinalityIndices(col)
```
**Arguments**
- `col` β A low cardinality column. [`LowCardinality`](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality)
**Returned value**
The position of the value in the dictionary of the current part. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage examples**
```
DROP TABLE IF EXISTS test;
CREATE TABLE test (s LowCardinality(String)) ENGINE = Memory;
-- create two parts:
INSERT INTO test VALUES ('ab'), ('cd'), ('ab'), ('ab'), ('df');
INSERT INTO test VALUES ('ef'), ('cd'), ('ab'), ('cd'), ('ef');
SELECT s, lowCardinalityIndices(s) FROM test;
```
```
ββsβββ¬βlowCardinalityIndices(s)ββ
β ab β 1 β
β cd β 2 β
β ab β 1 β
β ab β 1 β
β df β 3 β
ββββββ΄βββββββββββββββββββββββββββ
ββsβββ¬βlowCardinalityIndices(s)ββ
β ef β 1 β
β cd β 2 β
β ab β 3 β
β cd β 2 β
β ef β 1 β
ββββββ΄βββββββββββββββββββββββββββ
```
## lowCardinalityKeys[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#lowCardinalityKeys "Direct link to lowCardinalityKeys")
Introduced in: v18.12.0
Returns the dictionary values of a [LowCardinality](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality) column. If the block is smaller or larger than the dictionary size, the result will be truncated or extended with default values. Since LowCardinality have per-part dictionaries, this function may return different dictionary values in different parts.
**Syntax**
```
lowCardinalityKeys(col)
```
**Arguments**
- `col` β A low cardinality column. [`LowCardinality`](https://clickhouse.com/docs/sql-reference/data-types/lowcardinality)
**Returned value**
Returns the dictionary keys. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**lowCardinalityKeys**
```
DROP TABLE IF EXISTS test;
CREATE TABLE test (s LowCardinality(String)) ENGINE = Memory;
-- create two parts:
INSERT INTO test VALUES ('ab'), ('cd'), ('ab'), ('ab'), ('df');
INSERT INTO test VALUES ('ef'), ('cd'), ('ab'), ('cd'), ('ef');
SELECT s, lowCardinalityKeys(s) FROM test;
```
```
ββsβββ¬βlowCardinalityKeys(s)ββ
β ef β β
β cd β ef β
β ab β cd β
β cd β ab β
β ef β β
ββββββ΄ββββββββββββββββββββββββ
ββsβββ¬βlowCardinalityKeys(s)ββ
β ab β β
β cd β ab β
β ab β cd β
β ab β df β
β df β β
ββββββ΄ββββββββββββββββββββββββ
```
## materialize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#materialize "Direct link to materialize")
Introduced in: v1.1.0
Turns a constant into a full column containing a single value. Full columns and constants are represented differently in memory. Functions usually execute different code for normal and constant arguments, although the result should typically be the same. This function can be used to debug this behavior.
**Syntax**
```
materialize(x)
```
**Arguments**
- `x` β A constant. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a full column containing the constant value. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
-- In the example below the `countMatches` function expects a constant second argument.
-- This behaviour can be debugged by using the `materialize` function to turn a constant into a full column,
-- verifying that the function throws an error for a non-constant argument.
SELECT countMatches('foobarfoo', 'foo');
SELECT countMatches('foobarfoo', materialize('foo'));
```
```
2
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Illegal type of argument #2 'pattern' of function countMatches, expected constant String, got String
```
## minSampleSizeContinuous[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#minSampleSizeContinuous "Direct link to minSampleSizeContinuous")
Introduced in: v23.10.0
Calculates the minimum required sample size for an A/B test comparing means of a continuous metric in two samples.
Uses the formula described in [this article](https://towardsdatascience.com/required-sample-size-for-a-b-testing-6f6608dd330a). Assumes equal sizes of treatment and control groups. Returns the required sample size for one group (i.e. the sample size required for the whole experiment is twice the returned value). Also assumes equal variance of the test metric in treatment and control groups.
**Syntax**
```
minSampleSizeContinuous(baseline, sigma, mde, power, alpha)
```
**Aliases**: `minSampleSizeContinous`
**Arguments**
- `baseline` β Baseline value of a metric. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `sigma` β Baseline standard deviation of a metric. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `mde` β Minimum detectable effect (MDE) as percentage of the baseline value (e.g. for a baseline value 112.25 the MDE 0.03 means an expected change to 112.25 Β± 112.25\*0.03). [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `power` β Required statistical power of a test (1 - probability of Type II error). [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `alpha` β Required significance level of a test (probability of Type I error). [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a named Tuple with 3 elements: `minimum_sample_size`, `detect_range_lower` and `detect_range_upper`. These are respectively: the required sample size, the lower bound of the range of values not detectable with the returned required sample size, calculated as `baseline * (1 - mde)`, and the upper bound of the range of values not detectable with the returned required sample size, calculated as `baseline * (1 + mde)` (Float64). [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**minSampleSizeContinuous**
```
SELECT minSampleSizeContinuous(112.25, 21.1, 0.03, 0.80, 0.05) AS sample_size
```
```
(616.2931945826209,108.8825,115.6175)
```
## minSampleSizeConversion[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#minSampleSizeConversion "Direct link to minSampleSizeConversion")
Introduced in: v22.6.0
Calculates minimum required sample size for an A/B test comparing conversions (proportions) in two samples.
Uses the formula described in [this article](https://towardsdatascience.com/required-sample-size-for-a-b-testing-6f6608dd330a). Assumes equal sizes of treatment and control groups. Returns the sample size required for one group (i.e. the sample size required for the whole experiment is twice the returned value).
**Syntax**
```
minSampleSizeConversion(baseline, mde, power, alpha)
```
**Arguments**
- `baseline` β Baseline conversion. [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `mde` β Minimum detectable effect (MDE) as percentage points (e.g. for a baseline conversion 0.25 the MDE 0.03 means an expected change to 0.25 Β± 0.03). [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `power` β Required statistical power of a test (1 - probability of Type II error). [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
- `alpha` β Required significance level of a test (probability of Type I error). [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns a named Tuple with 3 elements: `minimum_sample_size`, `detect_range_lower`, `detect_range_upper`. These are, respectively: the required sample size, the lower bound of the range of values not detectable with the returned required sample size, calculated as `baseline - mde`, the upper bound of the range of values not detectable with the returned required sample size, calculated as `baseline + mde`. [`Tuple(Float64, Float64, Float64)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**minSampleSizeConversion**
```
SELECT minSampleSizeConversion(0.25, 0.03, 0.80, 0.05) AS sample_size
```
```
(3396.077603219163,0.22,0.28)
```
## neighbor[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#neighbor "Direct link to neighbor")
Introduced in: v20.1.0
Returns a value from a column at a specified offset from the current row. This function is deprecated and error-prone because it operates on the physical order of data blocks which may not correspond to the logical order expected by users. Consider using proper window functions instead.
The function can be enabled by setting `allow_deprecated_error_prone_window_functions = 1`.
**Syntax**
```
neighbor(column, offset[, default_value])
```
**Arguments**
- `column` β The source column. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
- `offset` β The offset from the current row. Positive values look forward, negative values look backward. [`Integer`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
- `default_value` β Optional. The value to return if the offset goes beyond the data bounds. If not specified, uses the default value for the column type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a value from the specified offset, or default if out of bounds. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT number, neighbor(number, 2) FROM system.numbers LIMIT 10;
```
```
ββnumberββ¬βneighbor(number, 2)ββ
β 0 β 2 β
β 1 β 3 β
β 2 β 4 β
β 3 β 5 β
β 4 β 6 β
β 5 β 7 β
β 6 β 8 β
β 7 β 9 β
β 8 β 0 β
β 9 β 0 β
ββββββββββ΄ββββββββββββββββββββββ
```
**With default value**
```
SELECT number, neighbor(number, 2, 999) FROM system.numbers LIMIT 10;
```
```
ββnumberββ¬βneighbor(number, 2, 999)ββ
β 0 β 2 β
β 1 β 3 β
β 2 β 4 β
β 3 β 5 β
β 4 β 6 β
β 5 β 7 β
β 6 β 8 β
β 7 β 9 β
β 8 β 999 β
β 9 β 999 β
ββββββββββ΄βββββββββββββββββββββββββββ
```
## normalizeQuery[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizeQuery "Direct link to normalizeQuery")
Introduced in: v20.8.0
Replaces literals, sequences of literals and complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with placeholder `?`.
**Syntax**
```
normalizeQuery(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the given sequence of characters with placeholders. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT normalizeQuery('[1, 2, 3, x]') AS query
```
```
ββqueryβββββ
β [?.., x] β
ββββββββββββ
```
## normalizeQueryKeepNames[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizeQueryKeepNames "Direct link to normalizeQueryKeepNames")
Introduced in: v21.2.0
Replaces literals and sequences of literals with placeholder `?` but does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs). This helps better analyze complex query logs.
**Syntax**
```
normalizeQueryKeepNames(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the given sequence of characters with placeholders. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT normalizeQuery('SELECT 1 AS aComplexName123'), normalizeQueryKeepNames('SELECT 1 AS aComplexName123')
```
```
ββnormalizeQuery('SELECT 1 AS aComplexName123')ββ¬βnormalizeQueryKeepNames('SELECT 1 AS aComplexName123')ββ
β SELECT ? AS `?` β SELECT ? AS aComplexName123 β
βββββββββββββββββββββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## normalizedQueryHash[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHash "Direct link to normalizedQueryHash")
Introduced in: v20.8.0
Returns identical 64 bit hash values without the values of literals for similar queries. Can be helpful in analyzing query logs.
**Syntax**
```
normalizedQueryHash(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a 64 bit hash value. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT normalizedQueryHash('SELECT 1 AS `xyz`') != normalizedQueryHash('SELECT 1 AS `abc`') AS res
```
```
ββresββ
β 1 β
βββββββ
```
## normalizedQueryHashKeepNames[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHashKeepNames "Direct link to normalizedQueryHashKeepNames")
Introduced in: v21.2.0
Like [`normalizedQueryHash`](https://clickhouse.com/docs/sql-reference/functions/other-functions#normalizedQueryHash) it returns identical 64 bit hash values without the values of literals for similar queries, but it does not replace complex aliases (containing whitespace, more than two digits or at least 36 bytes long such as UUIDs) with a placeholder before hashing. Can be helpful in analyzing query logs.
**Syntax**
```
normalizedQueryHashKeepNames(x)
```
**Arguments**
- `x` β Sequence of characters. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a 64 bit hash value. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT normalizedQueryHash('SELECT 1 AS `xyz123`') != normalizedQueryHash('SELECT 1 AS `abc123`') AS normalizedQueryHash;
SELECT normalizedQueryHashKeepNames('SELECT 1 AS `xyz123`') != normalizedQueryHashKeepNames('SELECT 1 AS `abc123`') AS normalizedQueryHashKeepNames;
```
```
ββnormalizedQueryHashββ
β 0 β
βββββββββββββββββββββββ
ββnormalizedQueryHashKeepNamesββ
β 1 β
ββββββββββββββββββββββββββββββββ
```
## parseReadableSize[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSize "Direct link to parseReadableSize")
Introduced in: v24.6.0
Given a string containing a byte size and `B`, `KiB`, `KB`, `MiB`, `MB`, etc. as a unit (i.e. [ISO/IEC 80000-13](https://en.wikipedia.org/wiki/ISO/IEC_80000) or decimal byte unit), this function returns the corresponding number of bytes. If the function is unable to parse the input value, it throws an exception.
The inverse operations of this function are [`formatReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize) and [`formatReadableDecimalSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize).
**Syntax**
```
parseReadableSize(x)
```
**Arguments**
- `x` β Readable size with ISO/IEC 80000-13 or decimal byte unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the number of bytes, rounded up to the nearest integer. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB']) AS readable_sizes, parseReadableSize(readable_sizes) AS sizes;
```
```
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
ββββββββββββββββββ΄ββββββββββ
```
## parseReadableSizeOrNull[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrNull "Direct link to parseReadableSizeOrNull")
Introduced in: v24.6.0
Given a string containing a byte size and `B`, `KiB`, `KB`, `MiB`, `MB`, etc. as a unit (i.e. [ISO/IEC 80000-13](https://en.wikipedia.org/wiki/ISO/IEC_80000) or decimal byte unit), this function returns the corresponding number of bytes. If the function is unable to parse the input value, it returns `NULL`.
The inverse operations of this function are [`formatReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize) and [`formatReadableDecimalSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize).
**Syntax**
```
parseReadableSizeOrNull(x)
```
**Arguments**
- `x` β Readable size with ISO/IEC 80000-13 or decimal byte unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the number of bytes, rounded up to the nearest integer, or `NULL` if unable to parse the input [`Nullable(UInt64)`](https://clickhouse.com/docs/sql-reference/data-types/nullable)
**Examples**
**Usage example**
```
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB', 'invalid']) AS readable_sizes, parseReadableSizeOrNull(readable_sizes) AS sizes;
```
```
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
β invalid β α΄Ία΅α΄Έα΄Έ β
ββββββββββββββββββ΄ββββββββββ
```
## parseReadableSizeOrZero[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseReadableSizeOrZero "Direct link to parseReadableSizeOrZero")
Introduced in: v24.6.0
Given a string containing a byte size and `B`, `KiB`, `KB`, `MiB`, `MB`, etc. as a unit (i.e. [ISO/IEC 80000-13](https://en.wikipedia.org/wiki/ISO/IEC_80000) or decimal byte unit), this function returns the corresponding number of bytes. If the function is unable to parse the input value, it returns `0`.
The inverse operations of this function are [`formatReadableSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableSize) and [`formatReadableDecimalSize`](https://clickhouse.com/docs/sql-reference/functions/other-functions#formatReadableDecimalSize).
**Syntax**
```
parseReadableSizeOrZero(x)
```
**Arguments**
- `x` β Readable size with ISO/IEC 80000-13 or decimal byte unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns the number of bytes, rounded up to the nearest integer, or `0` if unable to parse the input. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT arrayJoin(['1 B', '1 KiB', '3 MB', '5.314 KiB', 'invalid']) AS readable_sizes, parseReadableSizeOrZero(readable_sizes) AS sizes;
```
```
ββreadable_sizesββ¬βββsizesββ
β 1 B β 1 β
β 1 KiB β 1024 β
β 3 MB β 3000000 β
β 5.314 KiB β 5442 β
β invalid β 0 β
ββββββββββββββββββ΄ββββββββββ
```
## parseTimeDelta[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#parseTimeDelta "Direct link to parseTimeDelta")
Introduced in: v22.7.0
Parse a sequence of numbers followed by something resembling a time unit.
The time delta string uses these time unit specifications:
- `years`, `year`, `yr`, `y`
- `months`, `month`, `mo`
- `weeks`, `week`, `w`
- `days`, `day`, `d`
- `hours`, `hour`, `hr`, `h`
- `minutes`, `minute`, `min`, `m`
- `seconds`, `second`, `sec`, `s`
- `milliseconds`, `millisecond`, `millisec`, `ms`
- `microseconds`, `microsecond`, `microsec`, `ΞΌs`, `Β΅s`, `us`
- `nanoseconds`, `nanosecond`, `nanosec`, `ns`
Multiple time units can be combined with separators (space, `;`, `-`, `+`, `,`, `:`).
The length of years and months are approximations: year is 365 days, month is 30.5 days.
**Syntax**
```
parseTimeDelta(timestr)
```
**Arguments**
- `timestr` β A sequence of numbers followed by something resembling a time unit. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
The number of seconds. [`Float64`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Examples**
**Usage example**
```
SELECT parseTimeDelta('11s+22min')
```
```
ββparseTimeDelta('11s+22min')ββ
β 1331 β
βββββββββββββββββββββββββββββββ
```
**Complex time units**
```
SELECT parseTimeDelta('1yr2mo')
```
```
ββparseTimeDelta('1yr2mo')ββ
β 36806400 β
ββββββββββββββββββββββββββββ
```
## partitionId[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#partitionId "Direct link to partitionId")
Introduced in: v21.4.0
Computes the [partition ID](https://clickhouse.com/docs/engines/table-engines/mergetree-family/custom-partitioning-key).
Note
This function is slow and should not be called for large numbers of rows.
**Syntax**
```
partitionId(column1[, column2, ...])
```
**Aliases**: `partitionID`
**Arguments**
- `column1, column2, ...` β Column for which to return the partition ID.
**Returned value**
Returns the partition ID that the row belongs to. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
DROP TABLE IF EXISTS tab;
CREATE TABLE tab
(
i int,
j int
)
ENGINE = MergeTree
PARTITION BY i
ORDER BY tuple();
INSERT INTO tab VALUES (1, 1), (1, 2), (1, 3), (2, 4), (2, 5), (2, 6);
SELECT i, j, partitionId(i), _partition_id FROM tab ORDER BY i, j;
```
```
ββiββ¬βjββ¬βpartitionId(i)ββ¬β_partition_idββ
β 1 β 1 β 1 β 1 β
β 1 β 2 β 1 β 1 β
β 1 β 3 β 1 β 1 β
β 2 β 4 β 2 β 2 β
β 2 β 5 β 2 β 2 β
β 2 β 6 β 2 β 2 β
βββββ΄ββββ΄βββββββββββββββββ΄ββββββββββββββββ
```
## queryID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#queryID "Direct link to queryID")
Introduced in: v21.9.0
Returns the ID of the current query. Other parameters of a query can be extracted from field `query_id` in the [`system.query_log`](https://clickhouse.com/docs/operations/system-tables/query_log) table.
In contrast to [`initialQueryID`](https://clickhouse.com/docs/sql-reference/functions/other-functions#initialQueryID) function, `queryID` can return different results on different shards.
**Syntax**
```
queryID()
```
**Aliases**: `query_id`
**Arguments**
- None.
**Returned value**
Returns the ID of the current query. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
CREATE TABLE tmp (str String) ENGINE = Log;
INSERT INTO tmp (*) VALUES ('a');
SELECT count(DISTINCT t) FROM (SELECT queryID() AS t FROM remote('127.0.0.{1..3}', currentDatabase(), 'tmp') GROUP BY queryID());
```
```
ββcount(DISTINCT t)ββ
β 3 β
βββββββββββββββββββββ
```
## revision[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#revision "Direct link to revision")
Introduced in: v22.7.0
Returns the current ClickHouse server revision.
**Syntax**
```
revision()
```
**Arguments**
- None.
**Returned value**
Returns the current ClickHouse server revision. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT revision()
```
```
ββrevision()ββ
β 54485 β
ββββββββββββββ
```
## rowNumberInAllBlocks[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#rowNumberInAllBlocks "Direct link to rowNumberInAllBlocks")
Introduced in: v1.1.0
Returns a unique row number for each row processed.
**Syntax**
```
rowNumberInAllBlocks()
```
**Arguments**
- None.
**Returned value**
Returns the ordinal number of the row in the data block starting from `0`. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT rowNumberInAllBlocks()
FROM
(
SELECT *
FROM system.numbers_mt
LIMIT 10
)
SETTINGS max_block_size = 2
```
```
ββrowNumberInAllBlocks()ββ
β 0 β
β 1 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 4 β
β 5 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 2 β
β 3 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 6 β
β 7 β
ββββββββββββββββββββββββββ
ββrowNumberInAllBlocks()ββ
β 8 β
β 9 β
ββββββββββββββββββββββββββ
```
## rowNumberInBlock[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#rowNumberInBlock "Direct link to rowNumberInBlock")
Introduced in: v1.1.0
For each [block](https://clickhouse.com/docs/development/architecture#block) processed by `rowNumberInBlock`, returns the number of the current row.
The returned number starts from 0 for each block.
**Syntax**
```
rowNumberInBlock()
```
**Arguments**
- None.
**Returned value**
Returns the ordinal number of the row in the data block starting from `0`. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT rowNumberInBlock()
FROM
(
SELECT *
FROM system.numbers_mt
LIMIT 10
) SETTINGS max_block_size = 2
```
```
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
ββrowNumberInBlock()ββ
β 0 β
β 1 β
ββββββββββββββββββββββ
```
## runningAccumulate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningAccumulate "Direct link to runningAccumulate")
Introduced in: v1.1.0
Accumulates the states of an aggregate function for each row of a data block.
**Syntax**
```
runningAccumulate(agg_state[, grouping])
```
**Arguments**
- `agg_state` β State of the aggregate function. [`AggregateFunction`](https://clickhouse.com/docs/sql-reference/data-types/aggregatefunction)
- `grouping` β Optional. Grouping key. The state of the function is reset if the `grouping` value is changed. It can be any of the supported data types for which the equality operator is defined. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the accumulated result for each row. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example with initializeAggregation**
```
WITH initializeAggregation('sumState', number) AS one_row_sum_state
SELECT
number,
finalizeAggregation(one_row_sum_state) AS one_row_sum,
runningAccumulate(one_row_sum_state) AS cumulative_sum
FROM numbers(5);
```
```
ββnumberββ¬βone_row_sumββ¬βcumulative_sumββ
β 0 β 0 β 0 β
β 1 β 1 β 1 β
β 2 β 2 β 3 β
β 3 β 3 β 6 β
β 4 β 4 β 10 β
ββββββββββ΄ββββββββββββββ΄βββββββββββββββββ
```
## runningConcurrency[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningConcurrency "Direct link to runningConcurrency")
Introduced in: v21.3.0
Calculates the number of concurrent events. Each event has a start time and an end time. The start time is included in the event, while the end time is excluded. Columns with a start time and an end time must be of the same data type. The function calculates the total number of active (concurrent) events for each event start time.
Requirements
Events must be ordered by the start time in ascending order. If this requirement is violated the function raises an exception. Every data block is processed separately. If events from different data blocks overlap then they can not be processed correctly.
**Syntax**
```
runningConcurrency(start, end)
```
**Arguments**
- `start` β A column with the start time of events. [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`DateTime64`](https://clickhouse.com/docs/sql-reference/data-types/datetime64)
- `end` β A column with the end time of events. [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`DateTime64`](https://clickhouse.com/docs/sql-reference/data-types/datetime64)
**Returned value**
Returns the number of concurrent events at each event start time. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT start, runningConcurrency(start, end) FROM example_table;
```
```
βββββββstartββ¬βrunningConcurrency(start, end)ββ
β 2025-03-03 β 1 β
β 2025-03-06 β 2 β
β 2025-03-07 β 3 β
β 2025-03-11 β 2 β
ββββββββββββββ΄βββββββββββββββββββββββββββββββββ
```
## runningDifference[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifference "Direct link to runningDifference")
Introduced in: v1.1.0
Calculates the difference between two consecutive row values in the data block. Returns `0` for the first row, and for subsequent rows the difference to the previous row.
The result of the function depends on the affected data blocks and the order of data in the block. The order of rows during calculation of `runningDifference()` can differ from the order of rows returned to the user. To prevent that you can create a subquery with [`ORDER BY`](https://clickhouse.com/docs/sql-reference/statements/select/order-by) and call the function from outside the subquery. Please note that the block size affects the result. The internal state of `runningDifference` state is reset for each new block.
**Syntax**
```
runningDifference(x)
```
**Arguments**
- `x` β Column for which to calculate the running difference. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the difference between consecutive values, with 0 for the first row.
**Examples**
**Usage example**
```
SELECT
EventID,
EventTime,
runningDifference(EventTime) AS delta
FROM
(
SELECT
EventID,
EventTime
FROM events
WHERE EventDate = '2025-11-24'
ORDER BY EventTime ASC
LIMIT 5
);
```
```
ββEventIDββ¬βββββββββββEventTimeββ¬βdeltaββ
β 1106 β 2025-11-24 00:00:04 β 0 β
β 1107 β 2025-11-24 00:00:05 β 1 β
β 1108 β 2025-11-24 00:00:05 β 0 β
β 1109 β 2025-11-24 00:00:09 β 4 β
β 1110 β 2025-11-24 00:00:10 β 1 β
βββββββββββ΄ββββββββββββββββββββββ΄ββββββββ
```
**Block size impact example**
```
SELECT
number,
runningDifference(number + 1) AS diff
FROM numbers(100000)
WHERE diff != 1;
```
```
ββnumberββ¬βdiffββ
β 0 β 0 β
ββββββββββ΄βββββββ
ββnumberββ¬βdiffββ
β 65536 β 0 β
ββββββββββ΄βββββββ
```
## runningDifferenceStartingWithFirstValue[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifferenceStartingWithFirstValue "Direct link to runningDifferenceStartingWithFirstValue")
Introduced in: v1.1.0
Calculates the difference between consecutive row values in a data block, but unlike [`runningDifference`](https://clickhouse.com/docs/sql-reference/functions/other-functions#runningDifference), it returns the actual value of the first row instead of `0`.
Deprecated
Only returns differences inside the currently processed data block. Because of this error-prone behavior, the function is deprecated. It is advised to use [window functions](https://clickhouse.com/docs/sql-reference/window-functions) instead.
You can use setting `allow_deprecated_error_prone_window_functions` to allow usage of this function.
**Syntax**
```
runningDifferenceStartingWithFirstValue(x)
```
**Arguments**
- `x` β Column for which to calculate the running difference. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the difference between consecutive values, with the first row's value for the first row. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
SELECT
number,
runningDifferenceStartingWithFirstValue(number) AS diff
FROM numbers(5);
```
```
ββnumberββ¬βdiffββ
β 0 β 0 β
β 1 β 1 β
β 2 β 1 β
β 3 β 1 β
β 4 β 1 β
ββββββββββ΄βββββββ
```
## serverUUID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#serverUUID "Direct link to serverUUID")
Introduced in: v20.1.0
Returns the random and unique UUID (v4) generated when the server is first started. The UUID is persisted, i.e. the second, third, etc. server start return the same UUID.
**Syntax**
```
serverUUID()
```
**Arguments**
- None.
**Returned value**
Returns the random UUID of the server. [`UUID`](https://clickhouse.com/docs/sql-reference/data-types/uuid)
**Examples**
**Usage example**
```
SELECT serverUUID();
```
```
ββserverUUID()ββββββββββββββββββββββββββββββ
β 7ccc9260-000d-4d5c-a843-5459abaabb5f β
ββββββββββββββββββββββββββββββββββββββββββββ
```
## shardCount[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#shardCount "Direct link to shardCount")
Introduced in: v21.9.0
Returns the total number of shards for a distributed query. If a query is not distributed then constant value `0` is returned.
**Syntax**
```
shardCount()
```
**Arguments**
- None.
**Returned value**
Returns the total number of shards or `0`. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
-- See shardNum() example above which also demonstrates shardCount()
CREATE TABLE shard_count_example (dummy UInt8)
ENGINE=Distributed(test_cluster_two_shards_localhost, system, one, dummy);
SELECT shardCount() FROM shard_count_example;
```
```
ββshardCount()ββ
β 2 β
β 2 β
ββββββββββββββββ
```
## shardNum[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#shardNum "Direct link to shardNum")
Introduced in: v21.9.0
Returns the index of a shard which processes a part of data in a distributed query. Indices begin from `1`. If a query is not distributed then a constant value `0` is returned.
**Syntax**
```
shardNum()
```
**Arguments**
- None.
**Returned value**
Returns the shard index or a constant `0`. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
CREATE TABLE shard_num_example (dummy UInt8)
ENGINE=Distributed(test_cluster_two_shards_localhost, system, one, dummy);
SELECT dummy, shardNum(), shardCount() FROM shard_num_example;
```
```
ββdummyββ¬βshardNum()ββ¬βshardCount()ββ
β 0 β 1 β 2 β
β 0 β 2 β 2 β
βββββββββ΄βββββββββββββ΄βββββββββββββββ
```
## showCertificate[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#showCertificate "Direct link to showCertificate")
Introduced in: v22.6.0
Shows information about the current server's Secure Sockets Layer (SSL) certificate if it has been configured. See [Configuring TLS](https://clickhouse.com/docs/guides/sre/tls/configuring-tls) for more information on how to configure ClickHouse to use OpenSSL certificates to validate connections.
**Syntax**
```
showCertificate()
```
**Arguments**
- None.
**Returned value**
Returns map of key-value pairs relating to the configured SSL certificate. [`Map(String, String)`](https://clickhouse.com/docs/sql-reference/data-types/map)
**Examples**
**Usage example**
```
SELECT showCertificate() FORMAT LineAsString;
```
```
{'version':'1','serial_number':'2D9071D64530052D48308473922C7ADAFA85D6C5','signature_algo':'sha256WithRSAEncryption','issuer':'/CN=marsnet.local CA','not_before':'May 7 17:01:21 2024 GMT','not_after':'May 7 17:01:21 2025 GMT','subject':'/CN=chnode1','pkey_algo':'rsaEncryption'}
```
## sleep[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleep "Direct link to sleep")
Introduced in: v1.1.0
Pauses the execution of a query by the specified number of seconds. The function is primarily used for testing and debugging purposes.
The `sleep()` function should generally not be used in production environments, as it can negatively impact query performance and system responsiveness. However, it can be useful in the following scenarios:
1. **Testing**: When testing or benchmarking ClickHouse, you may want to simulate delays or introduce pauses to observe how the system behaves under certain conditions.
2. **Debugging**: If you need to examine the state of the system or the execution of a query at a specific point in time, you can use `sleep()` to introduce a pause, allowing you to inspect or collect relevant information.
3. **Simulation**: In some cases, you may want to simulate real-world scenarios where delays or pauses occur, such as network latency or external system dependencies.
Note
It's important to use the `sleep()` function judiciously and only when necessary, as it can potentially impact the overall performance and responsiveness of your ClickHouse system.
For security reasons, the function can only be executed in the default user profile (with `allow_sleep` enabled).
**Syntax**
```
sleep(seconds)
```
**Arguments**
- `seconds` β The number of seconds to pause the query execution to a maximum of 3 seconds. It can be a floating-point value to specify fractional seconds. [`const UInt*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`const Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns `0`. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
-- This query will pause for 2 seconds before completing.
-- During this time, no results will be returned, and the query will appear to be hanging or unresponsive.
SELECT sleep(2);
```
```
ββsleep(2)ββ
β 0 β
ββββββββββββ
1 row in set. Elapsed: 2.012 sec.
```
## sleepEachRow[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleepEachRow "Direct link to sleepEachRow")
Introduced in: v1.1.0
Pauses the execution of a query for a specified number of seconds for each row in the result set.
The `sleepEachRow()` function is primarily used for testing and debugging purposes, similar to the [`sleep()`](https://clickhouse.com/docs/sql-reference/functions/other-functions#sleep) function. It allows you to simulate delays or introduce pauses in the processing of each row, which can be useful in scenarios such as:
1. **Testing**: When testing or benchmarking ClickHouse's performance under specific conditions, you can use `sleepEachRow()` to simulate delays or introduce pauses for each row processed.
2. **Debugging**: If you need to examine the state of the system or the execution of a query for each row processed, you can use `sleepEachRow()` to introduce pauses, allowing you to inspect or collect relevant information.
3. **Simulation**: In some cases, you may want to simulate real-world scenarios where delays or pauses occur for each row processed, such as when dealing with external systems or network latencies.
Note
Like the `sleep()` function, it's important to use `sleepEachRow()` judiciously and only when necessary, as it can significantly impact the overall performance and responsiveness of your ClickHouse system, especially when dealing with large result sets.
**Syntax**
```
sleepEachRow(seconds)
```
**Arguments**
- `seconds` β The number of seconds to pause the query execution for each row in the result set to a maximum of 3 seconds. It can be a floating-point value to specify fractional seconds. [`const UInt*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`const Float*`](https://clickhouse.com/docs/sql-reference/data-types/float)
**Returned value**
Returns `0` for each row. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
-- The output will be delayed, with a 0.5-second pause between each row.
SELECT number, sleepEachRow(0.5) FROM system.numbers LIMIT 5;
```
```
ββnumberββ¬βsleepEachRow(0.5)ββ
β 0 β 0 β
β 1 β 0 β
β 2 β 0 β
β 3 β 0 β
β 4 β 0 β
ββββββββββ΄ββββββββββββββββββββ
```
## structureToCapnProtoSchema[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#structureToCapnProtoSchema "Direct link to structureToCapnProtoSchema")
Introduced in: v23.8.0
Function that converts ClickHouse table structure to CapnProto format schema
**Syntax**
```
structureToCapnProtoSchema(table_structure, message)
```
**Arguments**
- None.
**Returned value**
**Examples**
**random**
```
SELECT structureToCapnProtoSchema('s String, x UInt32', 'MessageName') format TSVRaw
```
```
struct MessageName
{
s @0 : Data;
x @1 : UInt32;
}
```
## structureToProtobufSchema[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#structureToProtobufSchema "Direct link to structureToProtobufSchema")
Introduced in: v23.8.0
Converts a ClickHouse table structure to Protobuf format schema.
This function takes a ClickHouse table structure definition and converts it into a Protocol Buffers (Protobuf) schema definition in proto3 syntax. This is useful for generating Protobuf schemas that match your ClickHouse table structures for data interchange.
**Syntax**
```
structureToProtobufSchema(structure, message_name)
```
**Arguments**
- `structure` β ClickHouse table structure definition as a string (e.g., 'column1 Type1, column2 Type2'). [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `message_name` β Name for the Protobuf message type in the generated schema. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Returned value**
Returns a Protobuf schema definition in proto3 syntax that corresponds to the input ClickHouse structure. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Converting ClickHouse structure to Protobuf schema**
```
SELECT structureToProtobufSchema('s String, x UInt32', 'MessageName') FORMAT TSVRaw;
```
```
syntax = "proto3";
message MessageName
{
bytes s = 1;
uint32 x = 2;
}
```
## tcpPort[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#tcpPort "Direct link to tcpPort")
Introduced in: v20.12.0
Returns the [native interface](https://clickhouse.com/docs/interfaces/tcp) TCP port number listened to by the server. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
tcpPort()
```
**Arguments**
- None.
**Returned value**
Returns the TCP port number. [`UInt16`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT tcpPort()
```
```
ββtcpPort()ββ
β 9000 β
βββββββββββββ
```
## throwIf[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#throwIf "Direct link to throwIf")
Introduced in: v1.1.0
Throw an exception if argument x is true. To use the `error_code` argument, configuration parameter `allow_custom_error_code_in_throw` must be enabled.
**Syntax**
```
throwIf(x[, message[, error_code]])
```
**Arguments**
- `x` β The condition to check. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
- `message` β Optional. Custom error message. [`const String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `error_code` β Optional. Custom error code. [`const Int8/16/32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Returned value**
Returns `0` if the condition is false, throws an exception if the condition is true. [`UInt8`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT throwIf(number = 3, 'Too many') FROM numbers(10);
```
```
β Progress: 0.00 rows, 0.00 B (0.00 rows/s., 0.00 B/s.) Received exception from server (version 19.14.1):
Code: 395. DB::Exception: Received from localhost:9000. DB::Exception: Too many.
```
## toColumnTypeName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#toColumnTypeName "Direct link to toColumnTypeName")
Introduced in: v1.1.0
Returns the internal name of the data type of the given value. Unlike function [`toTypeName`](https://clickhouse.com/docs/sql-reference/functions/other-functions#toTypeName), the returned data type potentially includes internal wrapper columns like `Const` and `LowCardinality`.
**Syntax**
```
toColumnTypeName(value)
```
**Arguments**
- `value` β Value for which to return the internal data type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the internal data type used to represent the value. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT toColumnTypeName(CAST('2025-01-01 01:02:03' AS DateTime));
```
```
ββtoColumnTypeName(CAST('2025-01-01 01:02:03', 'DateTime'))ββ
β Const(UInt32) β
βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## toTypeName[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#toTypeName "Direct link to toTypeName")
Introduced in: v1.1.0
Returns the type name of the passed argument. If `NULL` is passed, the function returns type `Nullable(Nothing)`, which corresponds to ClickHouse's internal `NULL` representation.
**Syntax**
```
toTypeName(x)
```
**Arguments**
- `x` β A value of arbitrary type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the data type name of the input value. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT toTypeName(123)
```
```
ββtoTypeName(123)ββ
β UInt8 β
βββββββββββββββββββ
```
## transactionID[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionID "Direct link to transactionID")
Introduced in: v22.6.0
Not supported in ClickHouse Cloud
Returns the ID of a transaction.
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your [configuration](https://clickhouse.com/docs/operations/configuration-files):
```
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
```
For more information see the page [Transactional (ACID) support](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
**Syntax**
```
transactionID()
```
**Arguments**
- None.
**Returned value**
Returns a tuple consisting of `start_csn`, `local_tid` and `host_id`.
- `start_csn`: Global sequential number, the newest commit timestamp that was seen when this transaction began.
- `local_tid`: Local sequential number that is unique for each transaction started by this host within a specific start\_csn.
- `host_id`: UUID of the host that has started this transaction. [`Tuple(UInt64, UInt64, UUID)`](https://clickhouse.com/docs/sql-reference/data-types/tuple)
**Examples**
**Usage example**
```
BEGIN TRANSACTION;
SELECT transactionID();
ROLLBACK;
```
```
ββtransactionID()βββββββββββββββββββββββββββββββββ
β (32,34,'0ee8b069-f2bb-4748-9eae-069c85b5252b') β
ββββββββββββββββββββββββββββββββββββββββββββββββββ
```
## transactionLatestSnapshot[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionLatestSnapshot "Direct link to transactionLatestSnapshot")
Introduced in: v22.6.0
Not supported in ClickHouse Cloud
Returns the newest snapshot (Commit Sequence Number) of a [transaction](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback) that is available for reading.
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your configuration:
```
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
```
For more information see the page [Transactional (ACID) support](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
**Syntax**
```
transactionLatestSnapshot()
```
**Arguments**
- None.
**Returned value**
Returns the latest snapshot (CSN) of a transaction. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
BEGIN TRANSACTION;
SELECT transactionLatestSnapshot();
ROLLBACK;
```
```
ββtransactionLatestSnapshot()ββ
β 32 β
βββββββββββββββββββββββββββββββ
```
## transactionOldestSnapshot[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transactionOldestSnapshot "Direct link to transactionOldestSnapshot")
Introduced in: v22.6.0
Not supported in ClickHouse Cloud
Returns the oldest snapshot (Commit Sequence Number) that is visible for some running [transaction](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
Note
This function is part of an experimental feature set. Enable experimental transaction support by adding this setting to your configuration:
```
<clickhouse>
<allow_experimental_transactions>1</allow_experimental_transactions>
</clickhouse>
```
For more information see the page [Transactional (ACID) support](https://clickhouse.com/docs/guides/developer/transactional#transactions-commit-and-rollback).
**Syntax**
```
transactionOldestSnapshot()
```
**Arguments**
- None.
**Returned value**
Returns the oldest snapshot (CSN) of a transaction. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
BEGIN TRANSACTION;
SELECT transactionOldestSnapshot();
ROLLBACK;
```
```
ββtransactionOldestSnapshot()ββ
β 32 β
βββββββββββββββββββββββββββββββ
```
## transform[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#transform "Direct link to transform")
Introduced in: v1.1.0
Transforms a value according to the explicitly defined mapping of some elements to other elements.
There are two variations of this function:
- `transform(x, array_from, array_to, default)` - transforms `x` using mapping arrays with a default value for unmatched elements
- `transform(x, array_from, array_to)` - same transformation but returns the original `x` if no match is found
The function searches for `x` in `array_from` and returns the corresponding element from `array_to` at the same index. If `x` is not found in `array_from`, it returns either the `default` value (4-parameter version) or the original `x` (3-parameter version). If multiple matching elements exist in `array_from`, it returns the element corresponding to the first match.
Requirements:
- `array_from` and `array_to` must have the same number of elements
- For 4-parameter version: `transform(T, Array(T), Array(U), U) -> U` where `T` and `U` can be different compatible types
- For 3-parameter version: `transform(T, Array(T), Array(T)) -> T` where all types must be the same
**Syntax**
```
transform(x, array_from, array_to[, default])
```
**Arguments**
- `x` β Value to transform. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
- `array_from` β Constant array of values to search for matches. [`Array((U)Int*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Decimal)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Float*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Date)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(DateTime)`](https://clickhouse.com/docs/sql-reference/data-types/array)
- `array_to` β Constant array of values to return for corresponding matches in `array_from`. [`Array((U)Int*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Decimal)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Float*)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(String)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(Date)`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Array(DateTime)`](https://clickhouse.com/docs/sql-reference/data-types/array)
- `default` β Optional. Value to return if `x` is not found in `array_from`. If omitted, returns x unchanged. [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime)
**Returned value**
Returns the corresponding value from `array_to` if x matches an element in `array_from`, otherwise returns default (if provided) or x (if default not provided). [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**transform(T, Array(T), Array(U), U) -\> U**
```
SELECT
transform(SearchEngineID, [2, 3], ['Yandex', 'Google'], 'Other') AS title,
count() AS c
FROM test.hits
WHERE SearchEngineID != 0
GROUP BY title
ORDER BY c DESC
```
```
ββtitleββββββ¬ββββββcββ
β Yandex β 498635 β
β Google β 229872 β
β Other β 104472 β
βββββββββββββ΄βββββββββ
```
**transform(T, Array(T), Array(T)) -\> T**
```
SELECT
transform(domain(Referer), ['yandex.ru', 'google.ru', 'vkontakte.ru'], ['www.yandex', 'example.com', 'vk.com']) AS s, count() AS c
FROM test.hits
GROUP BY domain(Referer)
ORDER BY count() DESC
LIMIT 10
```
```
ββsβββββββββββββββ¬βββββββcββ
β β 2906259 β
β www.yandex β 867767 β
β βββββββ.ru β 313599 β
β mail.yandex.ru β 107147 β
β ββββββ.ru β 100355 β
β βββββββββ.ru β 65040 β
β news.yandex.ru β 64515 β
β ββββββ.net β 59141 β
β example.com β 57316 β
ββββββββββββββββββ΄ββββββββββ
```
## uniqThetaIntersect[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaIntersect "Direct link to uniqThetaIntersect")
Introduced in: v22.9.0
Two uniqThetaSketch objects to do intersect calculation(set operation β©), the result is a new uniqThetaSketch.
**Syntax**
```
uniqThetaIntersect(uniqThetaSketch,uniqThetaSketch)
```
**Arguments**
- `uniqThetaSketch` β uniqThetaSketch object. [`Tuple`](https://clickhouse.com/docs/sql-reference/data-types/tuple) or [`Array`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
A new uniqThetaSketch containing the intersect result. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(uniqThetaIntersect(a, b)) AS a_intersect_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [1, 2]) AS a, arrayReduce('uniqThetaState', [2, 3, 4]) AS b);
```
```
ββa_intersect_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 1 β 2 β 3 β
βββββββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
```
## uniqThetaNot[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaNot "Direct link to uniqThetaNot")
Introduced in: v22.9.0
Two uniqThetaSketch objects to do a\_not\_b calculation(set operation Γ), the result is a new uniqThetaSketch.
**Syntax**
```
uniqThetaNot(uniqThetaSketch,uniqThetaSketch)
```
**Arguments**
- `uniqThetaSketch` β uniqThetaSketch object. [`Tuple`](https://clickhouse.com/docs/sql-reference/data-types/tuple) or [`Array`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns a new uniqThetaSketch containing the a\_not\_b result. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(uniqThetaNot(a, b)) AS a_not_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [2, 3, 4]) AS a, arrayReduce('uniqThetaState', [1, 2]) AS b);
```
```
ββa_not_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 2 β 3 β 2 β
βββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
```
## uniqThetaUnion[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uniqThetaUnion "Direct link to uniqThetaUnion")
Introduced in: v22.9.0
Two uniqThetaSketch objects to do union calculation(set operation βͺ), the result is a new uniqThetaSketch.
**Syntax**
```
uniqThetaUnion(uniqThetaSketch,uniqThetaSketch)
```
**Arguments**
- `uniqThetaSketch` β uniqThetaSketch object. [`Tuple`](https://clickhouse.com/docs/sql-reference/data-types/tuple) or [`Array`](https://clickhouse.com/docs/sql-reference/data-types/array) or [`Date`](https://clickhouse.com/docs/sql-reference/data-types/date) or [`DateTime`](https://clickhouse.com/docs/sql-reference/data-types/datetime) or [`String`](https://clickhouse.com/docs/sql-reference/data-types/string) or [`(U)Int*`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) or [`Float*`](https://clickhouse.com/docs/sql-reference/data-types/float) or [`Decimal`](https://clickhouse.com/docs/sql-reference/data-types/decimal)
**Returned value**
Returns a new uniqThetaSketch containing the union result. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT finalizeAggregation(uniqThetaUnion(a, b)) AS a_union_b, finalizeAggregation(a) AS a_cardinality, finalizeAggregation(b) AS b_cardinality
FROM
(SELECT arrayReduce('uniqThetaState', [1, 2]) AS a, arrayReduce('uniqThetaState', [2, 3, 4]) AS b);
```
```
ββa_union_bββ¬βa_cardinalityββ¬βb_cardinalityββ
β 4 β 2 β 3 β
βββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββ
```
## uptime[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#uptime "Direct link to uptime")
Introduced in: v1.1.0
Returns the server's uptime in seconds. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise it produces a constant value.
**Syntax**
```
uptime()
```
**Arguments**
- None.
**Returned value**
Returns the server uptime in seconds. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT uptime() AS Uptime
```
```
ββUptimeββ
β 55867 β
ββββββββββ
```
## variantElement[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#variantElement "Direct link to variantElement")
Introduced in: v25.2.0
Extracts a column with specified type from a `Variant` column.
**Syntax**
```
variantElement(variant, type_name[, default_value])
```
**Arguments**
- `variant` β Variant column. [`Variant`](https://clickhouse.com/docs/sql-reference/data-types/variant)
- `type_name` β The name of the variant type to extract. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
- `default_value` β The default value that will be used if variant doesn't have variant with specified type. Can be any type. Optional. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns a column with the specified variant type extracted from the Variant column. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Examples**
**Usage example**
```
CREATE TABLE test (v Variant(UInt64, String, Array(UInt64))) ENGINE = Memory;
INSERT INTO test VALUES (NULL), (42), ('Hello, World!'), ([1, 2, 3]);
SELECT v, variantElement(v, 'String'), variantElement(v, 'UInt64'), variantElement(v, 'Array(UInt64)') FROM test;
```
```
ββvββββββββββββββ¬βvariantElement(v, 'String')ββ¬βvariantElement(v, 'UInt64')ββ¬βvariantElement(v, 'Array(UInt64)')ββ
β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β [] β
β 42 β α΄Ία΅α΄Έα΄Έ β 42 β [] β
β Hello, World! β Hello, World! β α΄Ία΅α΄Έα΄Έ β [] β
β [1,2,3] β α΄Ία΅α΄Έα΄Έ β α΄Ία΅α΄Έα΄Έ β [1,2,3] β
βββββββββββββββββ΄ββββββββββββββββββββββββββββββ΄ββββββββββββββββββββββββββββββ΄βββββββββββββββββββββββββββββββββββββ
```
## variantType[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#variantType "Direct link to variantType")
Introduced in: v24.2.0
Returns the variant type name for each row of `Variant` column. If row contains NULL, it returns 'None' for it.
**Syntax**
```
variantType(variant)
```
**Arguments**
- `variant` β Variant column. [`Variant`](https://clickhouse.com/docs/sql-reference/data-types/variant)
**Returned value**
Returns an Enum column with variant type name for each row. [`Enum`](https://clickhouse.com/docs/sql-reference/data-types/enum)
**Examples**
**Usage example**
```
CREATE TABLE test (v Variant(UInt64, String, Array(UInt64))) ENGINE = Memory;
INSERT INTO test VALUES (NULL), (42), ('Hello, World!'), ([1, 2, 3]);
SELECT variantType(v) FROM test;
```
```
ββvariantType(v)ββ
β None β
β UInt64 β
β String β
β Array(UInt64) β
ββββββββββββββββββ
```
## version[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#version "Direct link to version")
Introduced in: v1.1.0
Returns the current version of ClickHouse as a string in the form: `major_version.minor_version.patch_version.number_of_commits_since_the_previous_stable_release`. If executed in the context of a distributed table, this function generates a normal column with values relevant to each shard. Otherwise, it produces a constant value.
**Syntax**
```
version()
```
**Arguments**
- None.
**Returned value**
Returns the current version of ClickHouse. [`String`](https://clickhouse.com/docs/sql-reference/data-types/string)
**Examples**
**Usage example**
```
SELECT version()
```
```
ββversion()ββ
β 24.2.1.1 β
βββββββββββββ
```
## visibleWidth[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#visibleWidth "Direct link to visibleWidth")
Introduced in: v1.1.0
Calculates the approximate width when outputting values to the console in text format (tab-separated). This function is used by the system to implement Pretty formats. `NULL` is represented as a string corresponding to `NULL` in Pretty formats.
**Syntax**
```
visibleWidth(x)
```
**Arguments**
- `x` β A value of any data type. [`Any`](https://clickhouse.com/docs/sql-reference/data-types)
**Returned value**
Returns the approximate width of the value when displayed in text format. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Calculate visible width of NULL**
```
SELECT visibleWidth(NULL)
```
```
ββvisibleWidth(NULL)ββ
β 4 β
ββββββββββββββββββββββ
```
## zookeeperSessionUptime[β](https://clickhouse.com/docs/sql-reference/functions/other-functions#zookeeperSessionUptime "Direct link to zookeeperSessionUptime")
Introduced in: v21.11.0
Returns the uptime of the current ZooKeeper session in seconds.
**Syntax**
```
zookeeperSessionUptime()
```
**Arguments**
- None.
**Returned value**
Returns the uptime of the current ZooKeeper session in seconds. [`UInt32`](https://clickhouse.com/docs/sql-reference/data-types/int-uint)
**Examples**
**Usage example**
```
SELECT zookeeperSessionUptime();
```
```
ββzookeeperSessionUptime()ββ
β 286 β
ββββββββββββββββββββββββββββ
``` |
| Shard | 89 (laksa) |
| Root Hash | 12633450985039531489 |
| Unparsed URL | com,clickhouse!/docs/sql-reference/functions/other-functions s443 |