> ## Documentation Index > Fetch the complete documentation index at: https://dune-pro-1110-add-delete-endpoints-python-js-docs.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Aggregate functions Aggregate functions operate on a set of values to compute a single result. Except for `count`, `count_if`, `max_by`, `min_by` and `approx_distinct`, all of these aggregate functions ignore null values and return null for no input rows or when all values are null. For example, `sum` returns null rather than zero and `avg` does not include null values in the count. The `coalesce` function can be used to convert null into zero. ## Ordering during aggregation Some aggregate functions such as `array_agg` produce different results depending on the order of input values. This ordering can be specified by writing an `order-by-clause` within the aggregate function: ```sql array_agg(x ORDER BY y DESC) array_agg(x ORDER BY x, y, z) ``` ## Filtering during aggregation The `FILTER` keyword can be used to remove rows from aggregation processing with a condition expressed using a `WHERE` clause. This is evaluated for each row before it is used in the aggregation and is supported for all aggregate functions. ```sql aggregate_function(...) FILTER (WHERE ) ``` A common and very useful example is to use `FILTER` to remove nulls from consideration when using `array_agg`: ```sql SELECT array_agg(name) FILTER (WHERE name IS NOT NULL) FROM region; ``` As another example, imagine you want to add a condition on the count for Iris flowers, modifying the following query: ```sql SELECT species, count(*) AS count FROM iris GROUP BY species; ``` ```text species | count -----------+------- setosa | 50 virginica | 50 versicolor | 50 ``` If you just use a normal `WHERE` statement you lose information: ```sql SELECT species, count(*) AS count FROM iris WHERE petal_length_cm > 4 GROUP BY species; ``` ```text species | count -----------+------- virginica | 50 versicolor | 34 ``` Using a filter you retain all information: ```sql SELECT species, count(*) FILTER (where petal_length_cm > 4) AS count FROM iris GROUP BY species; ``` ```text species | count -----------+------- virginica | 50 setosa | 0 versicolor | 34 ``` ## General aggregate functions #### arbitrary() **`arbitrary(x)`** → \[same as input] Returns an arbitrary non-null value of `x`, if one exists. #### any\_value() **`any_value(x)`** → \[same as input] Returns an arbitrary non-null value of `x`, if one exists. This is an alias for `arbitrary`. #### array\_agg() **`array_agg(x)`** → \[same as input] Returns an array created from the input `x` elements. #### avg() **`avg(x)`** → double Returns the average (arithmetic mean) of all input values. **`avg(time interval type)`** → time interval type Returns the average interval length of all input values. #### bool\_and() **`bool_and(boolean)`** → boolean Returns `TRUE` if every input value is `TRUE`, otherwise `FALSE`. #### bool\_or() **`bool_or(boolean)`** → boolean Returns `TRUE` if any input value is `TRUE`, otherwise `FALSE`. #### checksum() **`checksum(x)`** → varbinary Returns an order-insensitive checksum of the given values. #### count() **`count(*)`** → bigint Returns the number of input rows. **`count(x)`** → bigint Returns the number of non-null input values. #### count\_if() **`count_if(x)`** → bigint Returns the number of `TRUE` input values. This function is equivalent to `count(CASE WHEN x THEN 1 END)`. #### every() **`every(boolean)`** → boolean This is an alias for `bool_and`. #### geometric\_mean() **`geometric_mean(x)`** → double Returns the geometric mean of all input values. #### listagg() **`listagg(x, separator)`** → varchar Returns the concatenated input values, separated by the `separator` string. Synopsis: ```sql LISTAGG( expression [, separator] [ON OVERFLOW overflow_behaviour]) WITHIN GROUP (ORDER BY sort_item, [...]) ``` If `separator` is not specified, the empty string will be used as `separator`. In its simplest form the function looks like: ```sql SELECT listagg(value, ',') WITHIN GROUP (ORDER BY value) csv_value FROM (VALUES 'a', 'c', 'b') t(value); ``` and results in: ```text csv_value ----------- 'a,b,c' ``` The overflow behaviour is by default to throw an error in case that the length of the output of the function exceeds `1048576` bytes: ```sql SELECT listagg(value, ',' ON OVERFLOW ERROR) WITHIN GROUP (ORDER BY value) csv_value FROM (VALUES 'a', 'c', 'b') t(value); ``` and results in: ```text csv_value ----------- 'a,c,b' ``` The overflow behaviour can also be to truncate the output: ```sql SELECT listagg(value, ',' ON OVERFLOW TRUNCATE) WITHIN GROUP (ORDER BY value) csv_value FROM (VALUES 'a', 'c', 'b') t(value); ``` and results in: ```text csv_value ----------- 'a,b' ``` The overflow behaviour can also be to skip the overflowed values: ```sql SELECT listagg(value, ',' ON OVERFLOW SKIP) WITHIN GROUP (ORDER BY value) csv_value ``` The current implementation of `LISTAGG` function does not support window frames. #### max() **`max(x)`** → \[same as input] Returns the maximum value of all input values. **`max(x, n)`** → array\<\[same as x]> Returns `n` largest values of all input values of `x`. #### max\_by() **`max_by(x, y)`** → \[same as x] Returns the value of `x` associated with the maximum value of `y` over all input values. **`max_by(x, y, n)`** → array\<\[same as x]> Returns `n` values of `x` associated with the `n` largest of all input values of `y` in descending order of `y`. #### min() **`min(x)`** → \[same as input] Returns the minimum value of all input values. **`min(x, n)`** → array\<\[same as x]> Returns `n` smallest values of all input values of `x`. #### min\_by() **`min_by(x, y)`** → \[same as x] Returns the value of `x` associated with the minimum value of `y` over all input values. **`min_by(x, y, n)`** → array\<\[same as x]> Returns `n` values of `x` associated with the `n` smallest of all input values of `y` in ascending order of `y`. #### sum() **`sum(x)`** → \[same as input] Returns the sum of all input values. #### try\_sum() **`try_sum(uint256)`** → uint256 Returns the sum of all input values, or null if an addition overflow occurred. ## Bitwise aggregate functions #### bitwise\_and\_agg() **`bitwise_and_agg(x)`** → bigint Returns the bitwise AND of all input values in 2's complement representation. #### bitwise\_or\_agg() **`bitwise_or_agg(x)`** → bigint Returns the bitwise OR of all input values in 2's complement representation. #### histogram() **`histogram(x)`** → map\ Returns a map containing the count of the number of times each input value occurs. #### map\_agg() **`map_agg(key, value)`** → map\ Returns a map created from the input `key` / `value` pairs. #### map\_union() **`map_union(x(K,V))`** → map\ Returns the union of all the input maps. If a key is found in multiple input maps, that key's value in the resulting map comes from an arbitrary input map. #### map\_union\_agg() **`map_union_agg(x(K,V))`** → map\ Returns the union of all the input maps. If a key is found in multiple input maps, that key's value in the resulting map comes from the last input map. #### multimap\_agg() **`multimap_agg(key, value)`** → multimap\ Returns a multimap created from the input `key` / `value` pairs. #### multimap\_union() **`multimap_union(x(K,V))`** → multimap\ Returns the union of all the input multimaps. If a key is found in multiple input multimaps, that key's values in the resulting multimap are the union of all the values from the input multimaps. ## Approximate aggregate functions #### approx\_distinct() **`approx_distinct(x)`** → bigint Returns the approximate number of distinct input values. This function provides an approximation of `count(DISTINCT x)`. Zero is returned if all input values are null. This function should produce a standard error of 2.3%, which is the standard deviation of the (approximately normal) error distribution over all possible sets. It does not guarantee an upper bound on the error for any specific input set. **`approx_distinct(x, e)`** → bigint Returns the approximate number of distinct input values. This function provides an approximation of `count(DISTINCT x)`. Zero is returned if all input values are null. This function should produce a standard error of no more than `e`, which is the standard deviation of the (approximately normal) error distribution over all possible sets. It does not guarantee an upper bound on the error for any specific input set. The current implementation of this function requires that `e` be in the range of 0.0040625 to 0.26000. #### approx\_most\_frequent() **`approx_most_frequent(x, k)`** → map\<\[same as x], bigint> Computes the top frequent values up to `buckets` elements approximately. Approximate estimation of the function enables us to pick up the frequent values with less memory. Larger `capacity` improves the accuracy of underlying algorithm with sacrificing the memory capacity. The returned value is a map containing the top elements with corresponding estimated frequency. The error of the function depends on the permutation of the values and its cardinality. We can set the capacity same as the cardinality of the underlying data to achieve the least error. `buckets` and `capacity` must be `bigint`. `value` can be numeric or string type. The function uses the stream summary data structure proposed in the paper [Efficient Computation of Frequent and Top-k Elements in Data Streams](https://www.cse.ust.hk/~raywong/comp5331/References/EfficientComputationOfFrequentAndTop-kElementsInDataStreams.pdf) by A. Metwalley, D. Agrawl and A. Abbadi. #### approx\_percentile() **`approx_percentile(x, percentage)`** → \[same as x] Returns the approximate percentile for all input values of `x` at the given `percentage`. The value of `percentage` must be between zero and one and must be constant for all input rows. **`approx_percentile(x, percentages)`** → array\<\[same as x]> Returns the approximate percentile for all input values of `x` at each of the specified percentages. Each element of the `percentages` array must be between zero and one, and the array must be constant for all input rows. **`approx_percentile(x, w, percentage)`** → \[same as x] Returns the approximate weighed percentile for all input values of `x` using the per-item weight `w` at the percentage `percentage`. Weights must be greater or equal to 1. Integer-value weights can be thought of as a replication count for the value `x` in the percentile set. The value of `percentage` must be between zero and one and must be constant for all input rows. **`approx_percentile(x, w, percentages)`** → array\<\[same as x]> Returns the approximate weighed percentile for all input values of `x` using the per-item weight `w` at each of the given percentages specified in the array. Weights must be greater or equal to 1. Integer-value weights can be thought of as a replication count for the value `x` in the percentile set. Each element of the `percentages` array must be between zero and one, and the array must be constant for all input rows. #### approx\_set() **`approx_set(x)`** → HyperLogLog See `hyperloglog`. #### merge() **`merge(x)`** → HyperLogLog See `hyperloglog`. **`merge(qdigest(T))`** → qdigest(T) See `qdigest`. **`merge(tdigest)`** → tdigest See `tdigest`. #### numeric\_histogram() **`numeric_histogram(buckets, value)`** → map\ Computes an approximate histogram with up to `buckets` number of buckets for all `value`s. This function is equivalent to the variant of `numeric_histogram` that takes a `weight`, with a per-item weight of `1`. **`numeric_histogram(buckets, value, weight)`** → map\ Computes an approximate histogram with up to `buckets` number of buckets for all `value`s with a per-item weight of `weight`. The algorithm is based loosely on: ```text Yael Ben-Haim and Elad Tom-Tov, "A streaming parallel decision tree algorithm", J. Machine Learning Research 11 (2010), pp. 849--872. ``` `buckets` must be a `bigint`. `value` and `weight` must be numeric. #### qdigest\_agg() **`qdigest_agg(x)`** → qdigest See [Quantile digest functions](/query-engine/Functions-and-operators/qdigest). #### qdigest\_agg() **`qdigest_agg(x, w)`** → qdigest See [Quantile digest functions](/query-engine/Functions-and-operators/qdigest). #### tdigest\_agg() **`tdigest_agg(x)`** → tdigest See [T-Digest functions](/query-engine/Functions-and-operators/tdigest). #### tdigest\_agg() **`tdigest_agg(x, w)`** → tdigest See [T-Digest functions](/query-engine/Functions-and-operators/tdigest). ## Statistical aggregate functions #### corr() **`corr(x, y)`** → double Returns correlation coefficient of input values. #### covar\_pop() **`covar_pop(y, x)`** → double Returns the population covariance of input values. #### covar\_samp() **`covar_samp(y, x)`** → double Returns the sample covariance of input values. #### kurtosis() **`kurtosis(x)`** → double Returns the excess kurtosis of all input values. Unbiased estimate using the following expression: ```text kurtosis(x) = n(n+1)/((n-1)(n-2)(n-3))sum[(x_i-mean)^4]/stddev(x)^4-3(n-1)^2/((n-2)(n-3)) ``` #### regr\_intercept() **`regr_intercept(y, x)`** → double Returns linear regression intercept of input values. `y` is the dependent value and `x` is the independent value. #### regr\_slope() **`regr_slope(y, x)`** → double Returns linear regression slope of input values. `y` is the dependent value and `x` is the independent value. #### skewness() **`skewness(x)`** → double Returns the skewness of all input values. Returns the Fisher’s moment coefficient of [skewness](https://en.wikipedia.org/wiki/Skewness) of all input values. #### stddev() **`stddev(x)`** → double Returns the standard deviation of all input values. #### stddev\_pop() **`stddev_pop(x)`** → double Returns the population standard deviation of all input values. #### stddev\_samp() **`stddev_samp(x)`** → double Returns the sample standard deviation of all input values. #### variance() **`variance(x)`** → double Returns the variance of all input values. #### var\_pop() **`var_pop(x)`** → double Returns the population variance of all input values. #### var\_samp() **`var_samp(x)`** → double Returns the sample variance of all input values. ## Lambda aggregate functions #### reduce\_agg() **`reduce_agg(inputValue T, initialState S, inputFunction(S, T, S), combineFunction(S, S, S))`** → S Reduces all input values into a single value. `inputFunction` will be invoked for each non-null input value. In addition to taking the input value, `inputFunction` takes the current state, initially `initialState`, and returns the new state. `combineFunction` will be invoked to combine two states into a new state. The final state is returned: ```sql SELECT id, reduce_agg(value, 0, (a, b) -> a + b, (a, b) -> a + b) FROM ( VALUES (1, 3), (1, 4), (1, 5), (2, 6), (2, 7) ) AS t(id, value) GROUP BY id; -- (1, 12) -- (2, 13) ``` ```sql SELECT id, reduce_agg(value, 1, (a, b) -> a * b, (a, b) -> a * b) FROM ( VALUES (1, 3), (1, 4), (1, 5), (2, 6), (2, 7) ) AS t(id, value) GROUP BY id; -- (1, 60) -- (2, 42) ``` The state type must be a boolean, integer, floating-point, or date/time/interval.