🕷️ Crawler Inspector

URL Lookup

Direct Parameter Lookup

Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 89 (from laksa112)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa089.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count\')), getAhrefsUnparsedNoserviceFromURL(\'https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count","crawl_time":1775260980,"first_indexed_time":1740105108,"http_code":200,"src_unparsed":"com,clickhouse!\/docs\/sql-reference\/aggregate-functions\/reference\/count s443","src_root_hash":"12633450985039531489","history_drop_reason":null,"meta_title":"count | ClickHouse Docs","meta_descriptions":["Counts the number of rows or not-NULL values."],"attrs_boilerpipe_text":"count\n\nIntroduced in: v1.1.0\nCounts the number of rows or not-NULL values.\nClickHouse supports the following syntaxes for\ncount\n:\ncount(expr)\nor\nCOUNT(DISTINCT expr)\n.\ncount()\nor\nCOUNT(*)\n. The\ncount()\nsyntax is ClickHouse-specific.\nDetails\nClickHouse supports the\nCOUNT(DISTINCT ...)\nsyntax.\nThe behavior of this construction depends on the\ncount_distinct_implementation\nsetting.\nIt defines which of the\nuniq*\nfunctions is used to perform the operation.\nThe default is the\nuniqExact\nfunction.\nThe\nSELECT count() FROM table\nquery is optimized by default using metadata from MergeTree.\nIf you need to use row-level security, disable optimization using the\noptimize_trivial_count_query\nsetting.\nHowever\nSELECT count(nullable_column) FROM table\nquery can be optimized by enabling the\noptimize_functions_to_subcolumns\nsetting.\nWith\noptimize_functions_to_subcolumns = 1\nthe function reads only\nnull\nsubcolumn instead of reading and processing the whole column data.\nThe query\nSELECT count(n) FROM table\ntransforms to\nSELECT sum(NOT n.null) FROM table\n.\nImproving COUNT(DISTINCT expr) performance\nIf your\nCOUNT(DISTINCT expr)\nquery is slow, consider adding a\nGROUP BY\nclause as this improves parallelization.\nYou can also use a\nprojection\nto create an index on the target column used with\nCOUNT(DISTINCT target_col)\n.\nSyntax\ncount\n(\n[\nexpr\n]\n)\nArguments\nexpr\n— Optional. An expression. The function counts how many times this expression returned not null.\nExpression\nReturned value\nReturns the a row count if the function is called without parameters, otherwise returns a count of how many times the passed expression returned not null.\nUInt64\nExamples\nBasic row count\nQuery\nSELECT\ncount\n(\n)\nFROM\nt\nResponse\n┌─count()─┐\n│       5 │\n└─────────┘\nCOUNT(DISTINCT) example\nQuery\n-- This example shows that `count(DISTINCT num)` is performed by the `uniqExact` function according to the `count_distinct_implementation` setting value.\nSELECT\nname\n,\nvalue\nFROM\nsystem\n.\nsettings\nWHERE\nname\n=\n'count_distinct_implementation'\n;\nSELECT\ncount\n(\nDISTINCT\nnum\n)\nFROM\nt\nResponse\n┌─name──────────────────────────┬─value─────┐\n│ count_distinct_implementation │ uniqExact │\n└───────────────────────────────┴───────────┘\n┌─uniqExact(num)─┐\n│              3 │\n└────────────────┘","attrs_markdown":"[Skip to main content](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count#__docusaurus_skipToContent_fallback)\n\n[![ClickHouse](https:\/\/clickhouse.com\/docs\/img\/ch_logo_docs.svg)](https:\/\/clickhouse.com\/)\n\n- [Products](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count)\n  \n  - [ClickHouse Cloud Best way to use ClickHouse. 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[Syntax](https:\/\/clickhouse.com\/docs\/sql-reference\/syntax)\n  - [Input and Output Formats](https:\/\/clickhouse.com\/docs\/sql-reference\/formats)\n  - [Data types](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types)\n  - [Statements](https:\/\/clickhouse.com\/docs\/sql-reference\/statements)\n  - [Operators](https:\/\/clickhouse.com\/docs\/sql-reference\/operators)\n- [Engines](https:\/\/clickhouse.com\/docs\/engines)\n  - [Database Engines](https:\/\/clickhouse.com\/docs\/engines\/database-engines)\n  - [Table Engines](https:\/\/clickhouse.com\/docs\/engines\/table-engines)\n- [Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/functions)\n  - [Regular functions](https:\/\/clickhouse.com\/docs\/sql-reference\/functions\/regular-functions)\n  - [Aggregate functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions)\n    - [Aggregate Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference)\n      - [aggThrow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/aggthrow)\n      - [analysisOfVariance](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/analysis_of_variance)\n      - [any](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/any)\n      - [anyHeavy](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/anyheavy)\n      - [anyLast](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/anylast)\n      - [approx\\_top\\_k](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/approxtopk)\n      - [approx\\_top\\_sum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/approxtopsum)\n      - [argAndMax](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argandmax)\n      - [argAndMin](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argandmin)\n      - [argMax](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argmax)\n      - [argMin](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argmin)\n      - [avg](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/avg)\n      - [avgWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/avgweighted)\n      - [boundingRatio](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/boundingRatio)\n      - [categoricalInformationValue](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/categoricalinformationvalue)\n      - [contingency](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/contingency)\n      - [corr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corr)\n      - [corrMatrix](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corrmatrix)\n      - [corrStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corrstable)\n      - [count](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count)\n      - [covarPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpop)\n      - [covarPopMatrix](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpopmatrix)\n      - [covarPopStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpopstable)\n      - [covarSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarsamp)\n      - [covarSampMatrix](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarsampmatrix)\n      - [covarSampStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarsampstable)\n      - [cramersV](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/cramersv)\n      - [cramersVBiasCorrected](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/cramersvbiascorrected)\n      - [deltaSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/deltasum)\n      - [deltaSumTimestamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/deltasumtimestamp)\n      - [distinctDynamicTypes](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/distinctdynamictypes)\n      - [distinctJSONPaths](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/distinctjsonpaths)\n      - [distinctJSONPathsAndTypes](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/distinctJSONPathsAndTypes)\n      - [entropy](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/entropy)\n      - [estimateCompressionRatio](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/estimateCompressionRatio)\n      - [exponentialMovingAverage](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialMovingAverage)\n      - [exponentialTimeDecayedAvg](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedAvg)\n      - [exponentialTimeDecayedCount](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedCount)\n      - [exponentialTimeDecayedMax](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedMax)\n      - [exponentialTimeDecayedSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedSum)\n      - [first\\_value](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/first_value)\n      - [flameGraph](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/flame_graph)\n      - [groupArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparray)\n      - [groupArrayArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparrayarray)\n      - [groupArrayInsertAt](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparrayinsertat)\n      - [groupArrayIntersect](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparrayintersect)\n      - [groupArrayLast](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraylast)\n      - [groupArrayMovingAvg](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraymovingavg)\n      - [groupArrayMovingSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraymovingsum)\n      - [groupArraySample](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraysample)\n      - [groupArraySorted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraysorted)\n      - [groupBitAnd](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitand)\n      - [groupBitOr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitor)\n      - [groupBitXor](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitxor)\n      - [groupBitmap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmap)\n      - [groupBitmapAnd](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmapand)\n      - [groupBitmapOr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmapor)\n      - [groupBitmapXor](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmapxor)\n      - [groupConcat](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupconcat)\n      - [groupUniqArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupuniqarray)\n      - [intervalLengthSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/intervalLengthSum)\n      - [kolmogorovSmirnovTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/kolmogorovsmirnovtest)\n      - [kurtPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/kurtpop)\n      - [kurtSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/kurtsamp)\n      - [largestTriangleThreeBuckets](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/largestTriangleThreeBuckets)\n      - [last\\_value](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/last_value)\n      - [mannWhitneyUTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/mannwhitneyutest)\n      - [max](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/max)\n      - [maxIntersections](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/maxintersections)\n      - [maxIntersectionsPosition](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/maxintersectionsposition)\n      - [maxMap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/maxmap)\n      - [meanZTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/meanztest)\n      - [median](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/median)\n      - [min](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/min)\n      - [minMap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/minmap)\n      - [quantile](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantile)\n      - [quantileBFloat16](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilebfloat16)\n      - [quantileDD](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileddsketch)\n      - [quantileDeterministic](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiledeterministic)\n      - [quantileExact Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileexact)\n      - [quantileExactExclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactExclusive)\n      - [quantileExactHigh](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactHigh)\n      - [quantileExactInclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactInclusive)\n      - [quantileExactLow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactLow)\n      - [quantileExactWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileexactweighted)\n      - [quantileExactWeightedInterpolated](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactWeightedInterpolated)\n      - [quantileGK](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileGK)\n      - [quantileInterpolatedWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileInterpolatedWeighted)\n      - [quantilePrometheusHistogram](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilePrometheusHistogram)\n      - [quantileTDigest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletdigest)\n      - [quantileTDigestWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletdigestweighted)\n      - [quantileTiming](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletiming)\n      - [quantileTimingWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletimingweighted)\n      - [quantiles Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiles)\n      - [quantilesExactExclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilesExactExclusive)\n      - [quantilesExactInclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilesExactInclusive)\n      - [quantilesGK](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilesGK)\n      - [quantilesTimingWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilestimingweighted)\n      - [rankCorr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/rankCorr)\n      - [simpleLinearRegression](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/simplelinearregression)\n      - [singleValueOrNull](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/singlevalueornull)\n      - [skewPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/skewpop)\n      - [skewSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/skewsamp)\n      - [sparkbar](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sparkbar)\n      - [stddevPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevpop)\n      - [stddevPopStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevpopstable)\n      - [stddevSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevsamp)\n      - [stddevSampStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevsampstable)\n      - [stochasticLinearRegression](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stochasticlinearregression)\n      - [stochasticLogisticRegression](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stochasticlogisticregression)\n      - [studentTTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/studentttest)\n      - [studentTTestOneSample](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/studentttestonesample)\n      - [sum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sum)\n      - [sumCount](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sumcount)\n      - [sumKahan](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sumkahan)\n      - [sumMapWithOverflow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/summapwithoverflow)\n      - [sumMap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/summap)\n      - [sumWithOverflow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sumwithoverflow)\n      - [theilsU](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/theilsu)\n      - [timeSeriesChangesToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesChangesToGrid)\n      - [timeSeriesDeltaToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesDeltaToGrid)\n      - [timeSeriesDerivToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesDerivToGrid)\n      - [timeSeriesGroupArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesGroupArray)\n      - [timeSeriesInstantDeltaToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesInstantDeltaToGrid)\n      - [timeSeriesInstantRateToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesInstantRateToGrid)\n      - [timeSeriesLastTwoSamples](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesLastTwoSamples)\n      - [timeSeriesPredictLinearToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesPredictLinearToGrid)\n      - [timeSeriesRateToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesRateToGrid)\n      - [timeSeriesResampleToGridWithStaleness](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesResampleToGridWithStaleness)\n      - [timeSeriesResetsToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesResetsToGrid)\n      - [topK](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/topk)\n      - [topKWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/topkweighted)\n      - [uniq](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniq)\n      - [uniqCombined](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqcombined)\n      - [uniqCombined64](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqcombined64)\n      - [uniqExact](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqexact)\n      - [uniqHLL12](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqhll12)\n      - [uniqTheta](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqthetasketch)\n      - [varPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varPop)\n      - [varPopStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varpopstable)\n      - [varSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varSamp)\n      - [varSampStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varsampstable)\n      - [welchTTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/welchttest)\n    - [Combinators](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/combinators)\n    - [Parametric](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/parametric-functions)\n    - [GROUPING](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/grouping_function)\n    - [Combinator examples](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count)\n  - [Table functions](https:\/\/clickhouse.com\/docs\/sql-reference\/table-functions)\n  - [Window functions](https:\/\/clickhouse.com\/docs\/sql-reference\/window-functions)\n- [Formats](https:\/\/clickhouse.com\/docs\/interfaces\/formats)\n- [Data Lakes](https:\/\/clickhouse.com\/docs\/sql-reference\/datalakes)\n\n- [Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/functions)\n- [Aggregate functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions)\n- [Aggregate Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference)\n- count\n\n[Edit this page](https:\/\/github.com\/ClickHouse\/ClickHouse\/tree\/master\/docs\/en\/sql-reference\/aggregate-functions\/reference\/count.md)\n\n# count\n## count[](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count#count \"Direct link to count\")\nIntroduced in: v1.1.0\n\nCounts the number of rows or not-NULL values.\n\nClickHouse supports the following syntaxes for `count`:\n\n- `count(expr)` or `COUNT(DISTINCT expr)`.\n- `count()` or `COUNT(*)`. The `count()` syntax is ClickHouse-specific.\n\n**Details**\n\nClickHouse supports the `COUNT(DISTINCT ...)` syntax. The behavior of this construction depends on the [`count_distinct_implementation`](https:\/\/clickhouse.com\/docs\/operations\/settings\/settings#count_distinct_implementation) setting. It defines which of the [uniq\\*](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniq) functions is used to perform the operation. The default is the [uniqExact](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqexact) function.\n\nThe `SELECT count() FROM table` query is optimized by default using metadata from MergeTree. If you need to use row-level security, disable optimization using the [`optimize_trivial_count_query`](https:\/\/clickhouse.com\/docs\/operations\/settings\/settings#optimize_trivial_count_query) setting.\n\nHowever `SELECT count(nullable_column) FROM table` query can be optimized by enabling the [`optimize_functions_to_subcolumns`](https:\/\/clickhouse.com\/docs\/operations\/settings\/settings#optimize_functions_to_subcolumns) setting. With `optimize_functions_to_subcolumns = 1` the function reads only [`null`](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types\/nullable#finding-null) subcolumn instead of reading and processing the whole column data. The query `SELECT count(n) FROM table` transforms to `SELECT sum(NOT n.null) FROM table`.\n\nImproving COUNT(DISTINCT expr) performance\n\nIf your `COUNT(DISTINCT expr)` query is slow, consider adding a [`GROUP BY`](https:\/\/clickhouse.com\/docs\/sql-reference\/statements\/select\/group-by) clause as this improves parallelization. You can also use a [projection](https:\/\/clickhouse.com\/docs\/sql-reference\/statements\/alter\/projection) to create an index on the target column used with `COUNT(DISTINCT target_col)`.\n\n**Syntax**\n```\ncount([expr])\n```\n**Arguments**\n\n- `expr` — Optional. An expression. The function counts how many times this expression returned not null. [`Expression`](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types\/special-data-types\/expression)\n\n**Returned value**\n\nReturns the a row count if the function is called without parameters, otherwise returns a count of how many times the passed expression returned not null. [`UInt64`](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types\/int-uint)\n\n**Examples**\n\n**Basic row count**\n\nQuery\n```\nSELECT count() FROM t\n```\n\nResponse\n```\n┌─count()─┐\n│       5 │\n└─────────┘\n```\n\n**COUNT(DISTINCT) example**\n\nQuery\n```\n-- This example shows that `count(DISTINCT num)` is performed by the `uniqExact` function according to the `count_distinct_implementation` setting value.\nSELECT name, value FROM system.settings WHERE name = 'count_distinct_implementation';\nSELECT count(DISTINCT num) FROM t\n```\n\nResponse\n```\n┌─name──────────────────────────┬─value─────┐\n│ count_distinct_implementation │ uniqExact │\n└───────────────────────────────┴───────────┘\n┌─uniqExact(num)─┐\n│              3 │\n└────────────────┘\n```\n\n[Previous corrStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corrstable)\n\n[Next covarPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpop)\n\n- [count](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count#count)\n\nWas this page helpful?\n\n###### Try ClickHouse Cloud for FREE\nSeparation of storage and compute, automatic scaling, built-in SQL console, and lots more. \\$300 in free credits when signing up.\n\n[Try it for Free](https:\/\/console.clickhouse.cloud\/signUp?loc=doc-card-banner&glxid=b63eb15c-3260-418b-80d4-ad2f5bacab2e&pagePath=%2Fdocs%2Fsql-reference%2Faggregate-functions%2Freference%2Fcount&origPath=%2Fdocs%2Fsql-reference%2Faggregate-functions%2Freference%2Fcount&utm_ga=GA1.1.1440556656.1775260982)\n\n© 2016–2026 ClickHouse, Inc.\n\n[Trademark](https:\/\/clickhouse.com\/legal\/trademark-policy)·[Privacy](https:\/\/clickhouse.com\/legal\/privacy-policy)·[Security](https:\/\/trust.clickhouse.com\/)·[Terms of Service](https:\/\/clickhouse.com\/legal\/agreements\/terms-of-service)\n\n![](https:\/\/static.scarf.sh\/a.png?x-pxid=e6377503-591b-4886-9398-e69c7fee0b91)\n\n© 2016–2026 ClickHouse, Inc.\n\n[Trademark](https:\/\/clickhouse.com\/legal\/trademark-policy)·[Privacy](https:\/\/clickhouse.com\/legal\/privacy-policy)·[Security](https:\/\/trust.clickhouse.com\/)·[Terms of Service](https:\/\/clickhouse.com\/legal\/agreements\/terms-of-service)\n\n![](https:\/\/static.scarf.sh\/a.png?x-pxid=e6377503-591b-4886-9398-e69c7fee0b91)\n\n[![ClickHouse](https:\/\/clickhouse.com\/docs\/img\/ch_logo_docs.svg)](https:\/\/clickhouse.com\/)\n\nEN\n\n- Get started▼\n- Cloud▼\n- Manage data▼\n- Server admin▼\n- Reference▼\n- Integrations▼\n- ClickStack▼\n- chDB▼\n- About▼\n\n[![ClickHouse](https:\/\/clickhouse.com\/docs\/img\/ch_logo_docs.svg)](https:\/\/clickhouse.com\/)\n\nEN\n\nmain-menu\n\n- Introduction▼\n  - [Syntax](https:\/\/clickhouse.com\/docs\/sql-reference\/syntax)\n  - [Input and Output Formats](https:\/\/clickhouse.com\/docs\/sql-reference\/formats)\n  - Data types▼\n  - Statements▼\n  - Operators▼\n- Engines▼\n- Functions▼\n  - Regular functions▼\n  - Aggregate functions▼\n    - Aggregate Functions▼\n      - [aggThrow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/aggthrow)\n      - [analysisOfVariance](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/analysis_of_variance)\n      - [any](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/any)\n      - [anyHeavy](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/anyheavy)\n      - [anyLast](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/anylast)\n      - [approx\\_top\\_k](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/approxtopk)\n      - [approx\\_top\\_sum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/approxtopsum)\n      - [argAndMax](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argandmax)\n      - [argAndMin](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argandmin)\n      - [argMax](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argmax)\n      - [argMin](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/argmin)\n      - [avg](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/avg)\n      - [avgWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/avgweighted)\n      - [boundingRatio](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/boundingRatio)\n      - [categoricalInformationValue](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/categoricalinformationvalue)\n      - [contingency](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/contingency)\n      - [corr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corr)\n      - [corrMatrix](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corrmatrix)\n      - [corrStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/corrstable)\n      - [count](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count)\n      - [covarPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpop)\n      - [covarPopMatrix](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpopmatrix)\n      - [covarPopStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarpopstable)\n      - [covarSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarsamp)\n      - [covarSampMatrix](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarsampmatrix)\n      - [covarSampStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/covarsampstable)\n      - [cramersV](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/cramersv)\n      - [cramersVBiasCorrected](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/cramersvbiascorrected)\n      - [deltaSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/deltasum)\n      - [deltaSumTimestamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/deltasumtimestamp)\n      - [distinctDynamicTypes](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/distinctdynamictypes)\n      - [distinctJSONPaths](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/distinctjsonpaths)\n      - [distinctJSONPathsAndTypes](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/distinctJSONPathsAndTypes)\n      - [entropy](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/entropy)\n      - [estimateCompressionRatio](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/estimateCompressionRatio)\n      - [exponentialMovingAverage](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialMovingAverage)\n      - [exponentialTimeDecayedAvg](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedAvg)\n      - [exponentialTimeDecayedCount](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedCount)\n      - [exponentialTimeDecayedMax](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedMax)\n      - [exponentialTimeDecayedSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/exponentialTimeDecayedSum)\n      - [first\\_value](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/first_value)\n      - [flameGraph](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/flame_graph)\n      - [groupArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparray)\n      - [groupArrayArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparrayarray)\n      - [groupArrayInsertAt](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparrayinsertat)\n      - [groupArrayIntersect](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparrayintersect)\n      - [groupArrayLast](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraylast)\n      - [groupArrayMovingAvg](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraymovingavg)\n      - [groupArrayMovingSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraymovingsum)\n      - [groupArraySample](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraysample)\n      - [groupArraySorted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/grouparraysorted)\n      - [groupBitAnd](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitand)\n      - [groupBitOr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitor)\n      - [groupBitXor](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitxor)\n      - [groupBitmap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmap)\n      - [groupBitmapAnd](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmapand)\n      - [groupBitmapOr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmapor)\n      - [groupBitmapXor](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupbitmapxor)\n      - [groupConcat](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupconcat)\n      - [groupUniqArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/groupuniqarray)\n      - [intervalLengthSum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/intervalLengthSum)\n      - [kolmogorovSmirnovTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/kolmogorovsmirnovtest)\n      - [kurtPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/kurtpop)\n      - [kurtSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/kurtsamp)\n      - [largestTriangleThreeBuckets](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/largestTriangleThreeBuckets)\n      - [last\\_value](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/last_value)\n      - [mannWhitneyUTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/mannwhitneyutest)\n      - [max](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/max)\n      - [maxIntersections](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/maxintersections)\n      - [maxIntersectionsPosition](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/maxintersectionsposition)\n      - [maxMap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/maxmap)\n      - [meanZTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/meanztest)\n      - [median](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/median)\n      - [min](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/min)\n      - [minMap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/minmap)\n      - [quantile](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantile)\n      - [quantileBFloat16](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilebfloat16)\n      - [quantileDD](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileddsketch)\n      - [quantileDeterministic](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiledeterministic)\n      - [quantileExact Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileexact)\n      - [quantileExactExclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactExclusive)\n      - [quantileExactHigh](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactHigh)\n      - [quantileExactInclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactInclusive)\n      - [quantileExactLow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactLow)\n      - [quantileExactWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileexactweighted)\n      - [quantileExactWeightedInterpolated](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileExactWeightedInterpolated)\n      - [quantileGK](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileGK)\n      - [quantileInterpolatedWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantileInterpolatedWeighted)\n      - [quantilePrometheusHistogram](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilePrometheusHistogram)\n      - [quantileTDigest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletdigest)\n      - [quantileTDigestWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletdigestweighted)\n      - [quantileTiming](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletiming)\n      - [quantileTimingWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiletimingweighted)\n      - [quantiles Functions](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantiles)\n      - [quantilesExactExclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilesExactExclusive)\n      - [quantilesExactInclusive](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilesExactInclusive)\n      - [quantilesGK](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilesGK)\n      - [quantilesTimingWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/quantilestimingweighted)\n      - [rankCorr](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/rankCorr)\n      - [simpleLinearRegression](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/simplelinearregression)\n      - [singleValueOrNull](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/singlevalueornull)\n      - [skewPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/skewpop)\n      - [skewSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/skewsamp)\n      - [sparkbar](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sparkbar)\n      - [stddevPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevpop)\n      - [stddevPopStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevpopstable)\n      - [stddevSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevsamp)\n      - [stddevSampStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stddevsampstable)\n      - [stochasticLinearRegression](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stochasticlinearregression)\n      - [stochasticLogisticRegression](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/stochasticlogisticregression)\n      - [studentTTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/studentttest)\n      - [studentTTestOneSample](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/studentttestonesample)\n      - [sum](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sum)\n      - [sumCount](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sumcount)\n      - [sumKahan](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sumkahan)\n      - [sumMapWithOverflow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/summapwithoverflow)\n      - [sumMap](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/summap)\n      - [sumWithOverflow](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/sumwithoverflow)\n      - [theilsU](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/theilsu)\n      - [timeSeriesChangesToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesChangesToGrid)\n      - [timeSeriesDeltaToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesDeltaToGrid)\n      - [timeSeriesDerivToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesDerivToGrid)\n      - [timeSeriesGroupArray](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesGroupArray)\n      - [timeSeriesInstantDeltaToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesInstantDeltaToGrid)\n      - [timeSeriesInstantRateToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesInstantRateToGrid)\n      - [timeSeriesLastTwoSamples](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesLastTwoSamples)\n      - [timeSeriesPredictLinearToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesPredictLinearToGrid)\n      - [timeSeriesRateToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesRateToGrid)\n      - [timeSeriesResampleToGridWithStaleness](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesResampleToGridWithStaleness)\n      - [timeSeriesResetsToGrid](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/timeSeriesResetsToGrid)\n      - [topK](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/topk)\n      - [topKWeighted](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/topkweighted)\n      - [uniq](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniq)\n      - [uniqCombined](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqcombined)\n      - [uniqCombined64](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqcombined64)\n      - [uniqExact](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqexact)\n      - [uniqHLL12](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqhll12)\n      - [uniqTheta](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqthetasketch)\n      - [varPop](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varPop)\n      - [varPopStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varpopstable)\n      - [varSamp](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varSamp)\n      - [varSampStable](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/varsampstable)\n      - [welchTTest](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/welchttest)\n    - [Combinators](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/combinators)\n    - [Parametric](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/parametric-functions)\n    - [GROUPING](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/grouping_function)\n    - Combinator examples▼\n  - Table functions▼\n  - Window functions▼\n- Formats▼\n- [Data Lakes](https:\/\/clickhouse.com\/docs\/sql-reference\/datalakes)","attrs_readable_markdown":"## count[](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/count#count \"Direct link to count\")\nIntroduced in: v1.1.0\n\nCounts the number of rows or not-NULL values.\n\nClickHouse supports the following syntaxes for `count`:\n\n- `count(expr)` or `COUNT(DISTINCT expr)`.\n- `count()` or `COUNT(*)`. The `count()` syntax is ClickHouse-specific.\n\n**Details**\n\nClickHouse supports the `COUNT(DISTINCT ...)` syntax. The behavior of this construction depends on the [`count_distinct_implementation`](https:\/\/clickhouse.com\/docs\/operations\/settings\/settings#count_distinct_implementation) setting. It defines which of the [uniq\\*](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniq) functions is used to perform the operation. The default is the [uniqExact](https:\/\/clickhouse.com\/docs\/sql-reference\/aggregate-functions\/reference\/uniqexact) function.\n\nThe `SELECT count() FROM table` query is optimized by default using metadata from MergeTree. If you need to use row-level security, disable optimization using the [`optimize_trivial_count_query`](https:\/\/clickhouse.com\/docs\/operations\/settings\/settings#optimize_trivial_count_query) setting.\n\nHowever `SELECT count(nullable_column) FROM table` query can be optimized by enabling the [`optimize_functions_to_subcolumns`](https:\/\/clickhouse.com\/docs\/operations\/settings\/settings#optimize_functions_to_subcolumns) setting. With `optimize_functions_to_subcolumns = 1` the function reads only [`null`](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types\/nullable#finding-null) subcolumn instead of reading and processing the whole column data. The query `SELECT count(n) FROM table` transforms to `SELECT sum(NOT n.null) FROM table`.\n\nImproving COUNT(DISTINCT expr) performance\n\nIf your `COUNT(DISTINCT expr)` query is slow, consider adding a [`GROUP BY`](https:\/\/clickhouse.com\/docs\/sql-reference\/statements\/select\/group-by) clause as this improves parallelization. You can also use a [projection](https:\/\/clickhouse.com\/docs\/sql-reference\/statements\/alter\/projection) to create an index on the target column used with `COUNT(DISTINCT target_col)`.\n\n**Syntax**\n```\ncount([expr])\n```\n**Arguments**\n\n- `expr` — Optional. An expression. The function counts how many times this expression returned not null. [`Expression`](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types\/special-data-types\/expression)\n\n**Returned value**\n\nReturns the a row count if the function is called without parameters, otherwise returns a count of how many times the passed expression returned not null. [`UInt64`](https:\/\/clickhouse.com\/docs\/sql-reference\/data-types\/int-uint)\n\n**Examples**\n\n**Basic row count**\n\nQuery\n```\nSELECT count() FROM t\n```\n\nResponse\n```\n┌─count()─┐\n│       5 │\n└─────────┘\n```\n\n**COUNT(DISTINCT) example**\n\nQuery\n```\n-- This example shows that `count(DISTINCT num)` is performed by the `uniqExact` function according to the `count_distinct_implementation` setting value.\nSELECT name, value FROM system.settings WHERE name = 'count_distinct_implementation';\nSELECT count(DISTINCT num) FROM t\n```\n\nResponse\n```\n┌─name──────────────────────────┬─value─────┐\n│ count_distinct_implementation │ uniqExact │\n└───────────────────────────────┴───────────┘\n┌─uniqExact(num)─┐\n│              3 │\n└────────────────┘\n```","meta_canonical":null}

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INDEXABLE

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CRAWLED

7 days ago

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HTTP status	PASS	`download_http_code = 200`	HTTP 200
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Page Details

Property	Value
URL	https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count
Last Crawled	2026-04-04 00:03:00 (7 days ago)
First Indexed	2025-02-21 02:31:48 (1 year ago)
HTTP Status Code	200
Meta Title	count \| ClickHouse Docs
Meta Description	Counts the number of rows or not-NULL values.
Meta Canonical	null
Boilerpipe Text	count Introduced in: v1.1.0 Counts the number of rows or not-NULL values. ClickHouse supports the following syntaxes for count : count(expr) or COUNT(DISTINCT expr) . count() or COUNT() . The count() syntax is ClickHouse-specific. Details ClickHouse supports the COUNT(DISTINCT ...) syntax. The behavior of this construction depends on the count_distinct_implementation setting. It defines which of the uniq functions is used to perform the operation. The default is the uniqExact function. The SELECT count() FROM table query is optimized by default using metadata from MergeTree. If you need to use row-level security, disable optimization using the optimize_trivial_count_query setting. However SELECT count(nullable_column) FROM table query can be optimized by enabling the optimize_functions_to_subcolumns setting. With optimize_functions_to_subcolumns = 1 the function reads only null subcolumn instead of reading and processing the whole column data. The query SELECT count(n) FROM table transforms to SELECT sum(NOT n.null) FROM table . Improving COUNT(DISTINCT expr) performance If your COUNT(DISTINCT expr) query is slow, consider adding a GROUP BY clause as this improves parallelization. You can also use a projection to create an index on the target column used with COUNT(DISTINCT target_col) . Syntax count ( [ expr ] ) Arguments expr — Optional. An expression. The function counts how many times this expression returned not null. Expression Returned value Returns the a row count if the function is called without parameters, otherwise returns a count of how many times the passed expression returned not null. UInt64 Examples Basic row count Query SELECT count ( ) FROM t Response ┌─count()─┐ │ 5 │ └─────────┘ COUNT(DISTINCT) example Query -- This example shows that `count(DISTINCT num)` is performed by the `uniqExact` function according to the `count_distinct_implementation` setting value. SELECT name , value FROM system . settings WHERE name = 'count_distinct_implementation' ; SELECT count ( DISTINCT num ) FROM t Response ┌─name──────────────────────────┬─value─────┐ │ count_distinct_implementation │ uniqExact │ └───────────────────────────────┴───────────┘ ┌─uniqExact(num)─┐ │ 3 │ └────────────────┘
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[corr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corr) - [corrMatrix](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corrmatrix) - [corrStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corrstable) - [count](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count) - [covarPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpop) - [covarPopMatrix](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpopmatrix) - [covarPopStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpopstable) - [covarSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarsamp) - [covarSampMatrix](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarsampmatrix) - [covarSampStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarsampstable) - [cramersV](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/cramersv) - [cramersVBiasCorrected](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/cramersvbiascorrected) - [deltaSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/deltasum) - [deltaSumTimestamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/deltasumtimestamp) - [distinctDynamicTypes](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/distinctdynamictypes) - [distinctJSONPaths](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/distinctjsonpaths) - [distinctJSONPathsAndTypes](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/distinctJSONPathsAndTypes) - [entropy](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/entropy) - [estimateCompressionRatio](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/estimateCompressionRatio) - [exponentialMovingAverage](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialMovingAverage) - [exponentialTimeDecayedAvg](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedAvg) - [exponentialTimeDecayedCount](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedCount) - [exponentialTimeDecayedMax](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedMax) - [exponentialTimeDecayedSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedSum) - [first\_value](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/first_value) - [flameGraph](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/flame_graph) - [groupArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparray) - [groupArrayArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparrayarray) - [groupArrayInsertAt](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparrayinsertat) - [groupArrayIntersect](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparrayintersect) - [groupArrayLast](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraylast) - [groupArrayMovingAvg](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraymovingavg) - [groupArrayMovingSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraymovingsum) - [groupArraySample](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraysample) - [groupArraySorted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraysorted) - [groupBitAnd](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitand) - [groupBitOr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitor) - [groupBitXor](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitxor) - [groupBitmap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmap) - [groupBitmapAnd](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmapand) - [groupBitmapOr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmapor) - [groupBitmapXor](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmapxor) - [groupConcat](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupconcat) - [groupUniqArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupuniqarray) - [intervalLengthSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/intervalLengthSum) - [kolmogorovSmirnovTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/kolmogorovsmirnovtest) - [kurtPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/kurtpop) - [kurtSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/kurtsamp) - [largestTriangleThreeBuckets](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/largestTriangleThreeBuckets) - [last\_value](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/last_value) - [mannWhitneyUTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/mannwhitneyutest) - [max](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/max) - [maxIntersections](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/maxintersections) - [maxIntersectionsPosition](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/maxintersectionsposition) - [maxMap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/maxmap) - [meanZTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/meanztest) - [median](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/median) - [min](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/min) - [minMap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/minmap) - [quantile](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantile) - [quantileBFloat16](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilebfloat16) - [quantileDD](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileddsketch) - [quantileDeterministic](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiledeterministic) - [quantileExact Functions](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileexact) - [quantileExactExclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactExclusive) - [quantileExactHigh](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactHigh) - [quantileExactInclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactInclusive) - [quantileExactLow](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactLow) - [quantileExactWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileexactweighted) - [quantileExactWeightedInterpolated](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactWeightedInterpolated) - [quantileGK](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileGK) - [quantileInterpolatedWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileInterpolatedWeighted) - [quantilePrometheusHistogram](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilePrometheusHistogram) - [quantileTDigest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletdigest) - [quantileTDigestWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletdigestweighted) - [quantileTiming](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletiming) - [quantileTimingWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletimingweighted) - [quantiles Functions](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiles) - [quantilesExactExclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilesExactExclusive) - [quantilesExactInclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilesExactInclusive) - [quantilesGK](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilesGK) - [quantilesTimingWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilestimingweighted) - [rankCorr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/rankCorr) - [simpleLinearRegression](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/simplelinearregression) - [singleValueOrNull](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/singlevalueornull) - [skewPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/skewpop) - [skewSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/skewsamp) - [sparkbar](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sparkbar) - [stddevPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevpop) - [stddevPopStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevpopstable) - [stddevSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevsamp) - [stddevSampStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevsampstable) - [stochasticLinearRegression](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stochasticlinearregression) - [stochasticLogisticRegression](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stochasticlogisticregression) - [studentTTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/studentttest) - [studentTTestOneSample](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/studentttestonesample) - [sum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sum) - [sumCount](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sumcount) - [sumKahan](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sumkahan) - [sumMapWithOverflow](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/summapwithoverflow) - [sumMap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/summap) - [sumWithOverflow](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sumwithoverflow) - [theilsU](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/theilsu) - [timeSeriesChangesToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesChangesToGrid) - [timeSeriesDeltaToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesDeltaToGrid) - [timeSeriesDerivToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesDerivToGrid) - [timeSeriesGroupArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesGroupArray) - [timeSeriesInstantDeltaToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesInstantDeltaToGrid) - [timeSeriesInstantRateToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesInstantRateToGrid) - [timeSeriesLastTwoSamples](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesLastTwoSamples) - [timeSeriesPredictLinearToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesPredictLinearToGrid) - [timeSeriesRateToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesRateToGrid) - [timeSeriesResampleToGridWithStaleness](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesResampleToGridWithStaleness) - [timeSeriesResetsToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesResetsToGrid) - [topK](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/topk) - [topKWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/topkweighted) - [uniq](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniq) - [uniqCombined](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqcombined) - [uniqCombined64](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqcombined64) - [uniqExact](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqexact) - [uniqHLL12](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqhll12) - [uniqTheta](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqthetasketch) - [varPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varPop) - [varPopStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varpopstable) - [varSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varSamp) - [varSampStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varsampstable) - [welchTTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/welchttest) - [Combinators](https://clickhouse.com/docs/sql-reference/aggregate-functions/combinators) - [Parametric](https://clickhouse.com/docs/sql-reference/aggregate-functions/parametric-functions) - [GROUPING](https://clickhouse.com/docs/sql-reference/aggregate-functions/grouping_function) - [Combinator examples](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count) - [Table functions](https://clickhouse.com/docs/sql-reference/table-functions) - [Window functions](https://clickhouse.com/docs/sql-reference/window-functions) - [Formats](https://clickhouse.com/docs/interfaces/formats) - [Data Lakes](https://clickhouse.com/docs/sql-reference/datalakes) - [Functions](https://clickhouse.com/docs/sql-reference/functions) - [Aggregate functions](https://clickhouse.com/docs/sql-reference/aggregate-functions) - [Aggregate Functions](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference) - count [Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/sql-reference/aggregate-functions/reference/count.md) # count ## count[](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count#count "Direct link to count") Introduced in: v1.1.0 Counts the number of rows or not-NULL values. ClickHouse supports the following syntaxes for `count`: - `count(expr)` or `COUNT(DISTINCT expr)`. - `count()` or `COUNT()`. The `count()` syntax is ClickHouse-specific. Details* ClickHouse supports the `COUNT(DISTINCT ...)` syntax. The behavior of this construction depends on the [`count_distinct_implementation`](https://clickhouse.com/docs/operations/settings/settings#count_distinct_implementation) setting. It defines which of the [uniq\](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniq) functions is used to perform the operation. The default is the [uniqExact](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqexact) function. The `SELECT count() FROM table` query is optimized by default using metadata from MergeTree. If you need to use row-level security, disable optimization using the [`optimize_trivial_count_query`](https://clickhouse.com/docs/operations/settings/settings#optimize_trivial_count_query) setting. However `SELECT count(nullable_column) FROM table` query can be optimized by enabling the [`optimize_functions_to_subcolumns`](https://clickhouse.com/docs/operations/settings/settings#optimize_functions_to_subcolumns) setting. With `optimize_functions_to_subcolumns = 1` the function reads only [`null`](https://clickhouse.com/docs/sql-reference/data-types/nullable#finding-null) subcolumn instead of reading and processing the whole column data. The query `SELECT count(n) FROM table` transforms to `SELECT sum(NOT n.null) FROM table`. Improving COUNT(DISTINCT expr) performance If your `COUNT(DISTINCT expr)` query is slow, consider adding a [`GROUP BY`](https://clickhouse.com/docs/sql-reference/statements/select/group-by) clause as this improves parallelization. You can also use a [projection](https://clickhouse.com/docs/sql-reference/statements/alter/projection) to create an index on the target column used with `COUNT(DISTINCT target_col)`. Syntax* ``` count([expr]) ``` Arguments - `expr` — Optional. An expression. The function counts how many times this expression returned not null. [`Expression`](https://clickhouse.com/docs/sql-reference/data-types/special-data-types/expression) Returned value Returns the a row count if the function is called without parameters, otherwise returns a count of how many times the passed expression returned not null. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) Examples Basic row count Query ``` SELECT count() FROM t ``` Response ``` ┌─count()─┐ │ 5 │ └─────────┘ ``` COUNT(DISTINCT) example Query ``` -- This example shows that `count(DISTINCT num)` is performed by the `uniqExact` function according to the `count_distinct_implementation` setting value. SELECT name, value FROM system.settings WHERE name = 'count_distinct_implementation'; SELECT count(DISTINCT num) FROM t ``` Response ``` ┌─name──────────────────────────┬─value─────┐ │ count_distinct_implementation │ uniqExact │ └───────────────────────────────┴───────────┘ ┌─uniqExact(num)─┐ │ 3 │ └────────────────┘ ``` [Previous corrStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corrstable) [Next covarPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpop) - [count](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count#count) Was this page helpful? ###### Try ClickHouse Cloud for FREE Separation of storage and compute, automatic scaling, built-in SQL console, and lots more. \$300 in free credits when signing up. 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[analysisOfVariance](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/analysis_of_variance) - [any](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/any) - [anyHeavy](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/anyheavy) - [anyLast](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/anylast) - [approx\_top\_k](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/approxtopk) - [approx\_top\_sum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/approxtopsum) - [argAndMax](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/argandmax) - [argAndMin](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/argandmin) - [argMax](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/argmax) - [argMin](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/argmin) - [avg](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/avg) - [avgWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/avgweighted) - [boundingRatio](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/boundingRatio) - [categoricalInformationValue](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/categoricalinformationvalue) - [contingency](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/contingency) - [corr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corr) - [corrMatrix](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corrmatrix) - [corrStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/corrstable) - [count](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count) - [covarPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpop) - [covarPopMatrix](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpopmatrix) - [covarPopStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarpopstable) - [covarSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarsamp) - [covarSampMatrix](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarsampmatrix) - [covarSampStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/covarsampstable) - [cramersV](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/cramersv) - [cramersVBiasCorrected](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/cramersvbiascorrected) - [deltaSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/deltasum) - [deltaSumTimestamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/deltasumtimestamp) - [distinctDynamicTypes](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/distinctdynamictypes) - [distinctJSONPaths](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/distinctjsonpaths) - [distinctJSONPathsAndTypes](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/distinctJSONPathsAndTypes) - [entropy](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/entropy) - [estimateCompressionRatio](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/estimateCompressionRatio) - [exponentialMovingAverage](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialMovingAverage) - [exponentialTimeDecayedAvg](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedAvg) - [exponentialTimeDecayedCount](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedCount) - [exponentialTimeDecayedMax](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedMax) - [exponentialTimeDecayedSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/exponentialTimeDecayedSum) - [first\_value](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/first_value) - [flameGraph](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/flame_graph) - [groupArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparray) - [groupArrayArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparrayarray) - [groupArrayInsertAt](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparrayinsertat) - [groupArrayIntersect](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparrayintersect) - [groupArrayLast](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraylast) - [groupArrayMovingAvg](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraymovingavg) - [groupArrayMovingSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraymovingsum) - [groupArraySample](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraysample) - [groupArraySorted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/grouparraysorted) - [groupBitAnd](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitand) - [groupBitOr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitor) - [groupBitXor](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitxor) - [groupBitmap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmap) - [groupBitmapAnd](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmapand) - [groupBitmapOr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmapor) - [groupBitmapXor](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupbitmapxor) - [groupConcat](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupconcat) - [groupUniqArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/groupuniqarray) - [intervalLengthSum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/intervalLengthSum) - [kolmogorovSmirnovTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/kolmogorovsmirnovtest) - [kurtPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/kurtpop) - [kurtSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/kurtsamp) - [largestTriangleThreeBuckets](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/largestTriangleThreeBuckets) - [last\_value](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/last_value) - [mannWhitneyUTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/mannwhitneyutest) - [max](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/max) - [maxIntersections](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/maxintersections) - [maxIntersectionsPosition](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/maxintersectionsposition) - [maxMap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/maxmap) - [meanZTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/meanztest) - [median](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/median) - [min](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/min) - [minMap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/minmap) - [quantile](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantile) - [quantileBFloat16](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilebfloat16) - [quantileDD](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileddsketch) - [quantileDeterministic](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiledeterministic) - [quantileExact Functions](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileexact) - [quantileExactExclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactExclusive) - [quantileExactHigh](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactHigh) - [quantileExactInclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactInclusive) - [quantileExactLow](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactLow) - [quantileExactWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileexactweighted) - [quantileExactWeightedInterpolated](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileExactWeightedInterpolated) - [quantileGK](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileGK) - [quantileInterpolatedWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantileInterpolatedWeighted) - [quantilePrometheusHistogram](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilePrometheusHistogram) - [quantileTDigest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletdigest) - [quantileTDigestWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletdigestweighted) - [quantileTiming](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletiming) - [quantileTimingWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiletimingweighted) - [quantiles Functions](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantiles) - [quantilesExactExclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilesExactExclusive) - [quantilesExactInclusive](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilesExactInclusive) - [quantilesGK](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilesGK) - [quantilesTimingWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/quantilestimingweighted) - [rankCorr](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/rankCorr) - [simpleLinearRegression](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/simplelinearregression) - [singleValueOrNull](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/singlevalueornull) - [skewPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/skewpop) - [skewSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/skewsamp) - [sparkbar](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sparkbar) - [stddevPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevpop) - [stddevPopStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevpopstable) - [stddevSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevsamp) - [stddevSampStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stddevsampstable) - [stochasticLinearRegression](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stochasticlinearregression) - [stochasticLogisticRegression](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/stochasticlogisticregression) - [studentTTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/studentttest) - [studentTTestOneSample](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/studentttestonesample) - [sum](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sum) - [sumCount](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sumcount) - [sumKahan](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sumkahan) - [sumMapWithOverflow](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/summapwithoverflow) - [sumMap](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/summap) - [sumWithOverflow](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/sumwithoverflow) - [theilsU](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/theilsu) - [timeSeriesChangesToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesChangesToGrid) - [timeSeriesDeltaToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesDeltaToGrid) - [timeSeriesDerivToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesDerivToGrid) - [timeSeriesGroupArray](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesGroupArray) - [timeSeriesInstantDeltaToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesInstantDeltaToGrid) - [timeSeriesInstantRateToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesInstantRateToGrid) - [timeSeriesLastTwoSamples](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesLastTwoSamples) - [timeSeriesPredictLinearToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesPredictLinearToGrid) - [timeSeriesRateToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesRateToGrid) - [timeSeriesResampleToGridWithStaleness](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesResampleToGridWithStaleness) - [timeSeriesResetsToGrid](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/timeSeriesResetsToGrid) - [topK](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/topk) - [topKWeighted](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/topkweighted) - [uniq](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniq) - [uniqCombined](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqcombined) - [uniqCombined64](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqcombined64) - [uniqExact](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqexact) - [uniqHLL12](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqhll12) - [uniqTheta](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqthetasketch) - [varPop](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varPop) - [varPopStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varpopstable) - [varSamp](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varSamp) - [varSampStable](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/varsampstable) - [welchTTest](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/welchttest) - [Combinators](https://clickhouse.com/docs/sql-reference/aggregate-functions/combinators) - [Parametric](https://clickhouse.com/docs/sql-reference/aggregate-functions/parametric-functions) - [GROUPING](https://clickhouse.com/docs/sql-reference/aggregate-functions/grouping_function) - Combinator examples▼ - Table functions▼ - Window functions▼ - Formats▼ - [Data Lakes](https://clickhouse.com/docs/sql-reference/datalakes)
Readable Markdown	## count[](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/count#count "Direct link to count") Introduced in: v1.1.0 Counts the number of rows or not-NULL values. ClickHouse supports the following syntaxes for `count`: - `count(expr)` or `COUNT(DISTINCT expr)`. - `count()` or `COUNT()`. The `count()` syntax is ClickHouse-specific. Details* ClickHouse supports the `COUNT(DISTINCT ...)` syntax. The behavior of this construction depends on the [`count_distinct_implementation`](https://clickhouse.com/docs/operations/settings/settings#count_distinct_implementation) setting. It defines which of the [uniq\](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniq) functions is used to perform the operation. The default is the [uniqExact](https://clickhouse.com/docs/sql-reference/aggregate-functions/reference/uniqexact) function. The `SELECT count() FROM table` query is optimized by default using metadata from MergeTree. If you need to use row-level security, disable optimization using the [`optimize_trivial_count_query`](https://clickhouse.com/docs/operations/settings/settings#optimize_trivial_count_query) setting. However `SELECT count(nullable_column) FROM table` query can be optimized by enabling the [`optimize_functions_to_subcolumns`](https://clickhouse.com/docs/operations/settings/settings#optimize_functions_to_subcolumns) setting. With `optimize_functions_to_subcolumns = 1` the function reads only [`null`](https://clickhouse.com/docs/sql-reference/data-types/nullable#finding-null) subcolumn instead of reading and processing the whole column data. The query `SELECT count(n) FROM table` transforms to `SELECT sum(NOT n.null) FROM table`. Improving COUNT(DISTINCT expr) performance If your `COUNT(DISTINCT expr)` query is slow, consider adding a [`GROUP BY`](https://clickhouse.com/docs/sql-reference/statements/select/group-by) clause as this improves parallelization. You can also use a [projection](https://clickhouse.com/docs/sql-reference/statements/alter/projection) to create an index on the target column used with `COUNT(DISTINCT target_col)`. Syntax* ``` count([expr]) ``` Arguments - `expr` — Optional. An expression. The function counts how many times this expression returned not null. [`Expression`](https://clickhouse.com/docs/sql-reference/data-types/special-data-types/expression) Returned value Returns the a row count if the function is called without parameters, otherwise returns a count of how many times the passed expression returned not null. [`UInt64`](https://clickhouse.com/docs/sql-reference/data-types/int-uint) Examples Basic row count Query ``` SELECT count() FROM t ``` Response ``` ┌─count()─┐ │ 5 │ └─────────┘ ``` COUNT(DISTINCT) example Query ``` -- This example shows that `count(DISTINCT num)` is performed by the `uniqExact` function according to the `count_distinct_implementation` setting value. SELECT name, value FROM system.settings WHERE name = 'count_distinct_implementation'; SELECT count(DISTINCT num) FROM t ``` Response ``` ┌─name──────────────────────────┬─value─────┐ │ count_distinct_implementation │ uniqExact │ └───────────────────────────────┴───────────┘ ┌─uniqExact(num)─┐ │ 3 │ └────────────────┘ ```
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