14.14. 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.
General Aggregate Functions
- arbitrary(x) → [same as input]
Returns an arbitrary non-null value of x, if one exists.
- array_agg(x) → array<[same as input]>
Returns an array created from the input x elements.
- avg(x) → double
Returns the average (arithmetic mean) of all input values.
- bool_and(boolean) → boolean
Returns TRUE if every input value is TRUE, otherwise FALSE.
- bool_or(boolean) → boolean
Returns TRUE if any input value is TRUE, otherwise FALSE.
- checksum(x) → varbinary
Returns an order-insensitive checksum of the given values.
- count(*) → bigint
Returns the number of input rows.
- count(x) → bigint
Returns the number of non-null input values.
- count_if(x) → bigint
Returns the number of TRUE input values. This function is equivalent to count(CASE WHEN x THEN 1 END).
- every(boolean) → boolean
This is an alias for bool_and().
- geometric_mean(x) → double
Returns the geometric mean of all input values.
- 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.
- 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.
- 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.
- 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.
- sum(x) → [same as input]
Returns the sum of all input values.
Map Aggregate Functions
- histogram(x) → map<K,bigint>
Returns a map containing the count of the number of times each input value occurs.
- map_agg(key, value) → map<K,V>
Returns a map created from the input key / value pairs.
- multimap_agg(key, value) → map<K,array<V>>
Returns a multimap created from the input key / value pairs. Each key can be associated with multiple values.
Approximate Aggregate Functions
- 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: [0.01150, 0.26000].
- 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 p. The weight must be an integer value of at least one. It is effectively a replication count for the value x in the percentile set. The value of p must be between zero and one and must be constant for all input rows.
- approx_percentile(x, w, percentage, accuracy) → [same as x]
Returns the approximate weighed percentile for all input values of x using the per-item weight w at the percentage p, with a maximum rank error of accuracy. The weight must be an integer value of at least one. It is effectively a replication count for the value x in the percentile set. The value of p must be between zero and one and must be constant for all input rows. accuracy must be a value greater than zero and less than one, and it 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. The weight must be an integer value of at least one. It is effectively a replication count for the value x in the percentile set. Each element of the array must be between zero and one, and the array must be constant for all input rows.
- numeric_histogram(buckets, value, weight) → map<double, double>
Computes an approximate histogram with up to buckets number of buckets for all values with a per-item weight of weight. The algorithm is based loosely on:
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.
- numeric_histogram(buckets, value) → map<double, double>
Computes an approximate histogram with up to buckets number of buckets for all values. This function is equivalent to the variant of numeric_histogram() that takes a weight, with a per-item weight of 1.
Statistical Aggregate Functions
- corr(y, x) → double
Returns correlation coefficient of input values.
- covar_pop(y, x) → double
Returns the population covariance of input values.
- covar_samp(y, x) → double
Returns the sample covariance of input values.
- regr_intercept(y, x) → double
Returns linear regression intercept of input values. y is the dependent value. x is the independent value.
- regr_slope(y, x) → double
Returns linear regression slope of input values. y is the dependent value. x is the independent value.
- stddev(x) → double
This is an alias for stddev_samp().
- stddev_pop(x) → double
Returns the population standard deviation of all input values.
- stddev_samp(x) → double
Returns the sample standard deviation of all input values.
- variance(x) → double
This is an alias for var_samp().
- var_pop(x) → double
Returns the population variance of all input values.
- var_samp(x) → double
Returns the sample variance of all input values.