Aggregate functions take a collection of values as input (contrasted with scalar functions, which take a single input). Aggregate functions are used to perform a summary operation on the set of input values.

The GROUP BY clause in SQL provides the basis for identifying the sets of parameter values. The set of rows with the same values for the GROUP BY columns produces the input parameters for each execution of the aggregate function, or in the absence of a GROUP BY clause, all rows from the query produce a single set of input parameters to the aggregate.

SQL supports the following aggregate functions for its intrinsic data types: