SQL: Aggregate functions

Aggregate functions can be used if either

• all (non analytical) selected columns consist of aggregate functions, or
• there is a group by statement.

An aggregate functions returns one record per group. This is different from an analytic function which returns a value for each record (and the value is still computed from multiple records).

The SQL standard defines five aggregate functions:

• min, max
• count
• sum
• avg

RDBMS Vendors might provide additional aggregate functions, such as

• group_concat(…), listagg(), list_agg(…) (see SQL feature T625)
• stddev(…), variance(…)