Aggregate functions

Aggregate functions can be used within the aggregate clause in XTQL, or the SELECT clause in SQL.

In line with the SQL spec (which XTDB also respects in XTQL queries):

• Except in the case of (row-count) / COUNT(*), null values in the column are removed before the aggregate is calculated.

• Without grouping columns, aggregate functions will always return exactly one row - if the input column is empty (after nulls have been removed), the result will be a single row containing a null value.

Numeric aggregate functions

XTQL	SQL
(avg xs)	AVG([ALL] xs)	average (mean)
(avg-distinct xs)	AVG(DISTINCT xs)	average (mean) of distinct values
(count xs)	COUNT([ALL] xs)	count
(count-distinct xs)	COUNT(DISTINCT xs)	count of distinct values
(row-count)	COUNT(*)	row count
(max xs)	MAX([ALL] xs)	maximum
(max-distinct xs)	MAX(DISTINCT xs)	maximum of distinct values
(min xs)	MIN([ALL] xs)	minimum
(min-distinct xs)	MIN(DISTINCT xs)	minimum of distinct values
(stddev-pop xs)	STDDEV_POP(xs)	population standard deviation
(stddev-samp xs)	STDDEV_SAMP(xs)	sample standard deviation
(sum xs)	SUM([ALL] xs)	sum
(sum-distinct xs)	SUM(DISTINCT xs)	sum of distinct values
(var-pop xs)	VAR_POP(xs)	population variance
(var-samp xs)	VAR_SAMP(xs)	sample variance

• min/max aggregates are not yet supported on string values.

Boolean aggregate functions

XTQL	SQL
(bool-and xs) (every xs)	BOOL_AND(xs) EVERY(xs)	true if all values are true; false otherwise
(bool-or xs)	BOOL_OR(xs)	false if all values are false; true otherwise

Composite-type aggregate functions

XTQL	SQL
(array-agg xs)	ARRAY_AGG(xs)	return an array of all of the input values