The pg_aggregate table stores information about aggregate functions. An aggregate function is a function that operates on a set of values (typically one column from each row that matches a query condition) and returns a single value computed from all these values. Typical aggregate functions are sum, count, and max. Each entry in pg_aggregate is an extension of an entry in pg_proc. The pg_proc entry carries the aggregate’s name, input and output data types, and other information that is similar to ordinary functions.

Table 1. pg_catalog.pg_aggregate

column type references description
aggfnoid regproc pg_proc.oid Aggregate function OID
aggtransfn regproc pg_proc.oid Transition function OID
aggprelimfn regproc   Preliminary function OID (zero if none)
aggfinalfn regproc pg_proc.oid Final function OID (zero if none)
agginitval text   The initial value of the transition state. This is a text field containing the initial value in its external string representation. If this field is NULL, the transition state value starts out NULL
agginvtransfn regproc pg_proc.oid The OID in pg_proc of the inverse function of aggtransfn
agginvprelimfn regproc pg_proc.oid The OID in pg_proc of the inverse function of aggprelimfn
aggordered boolean   If true, the aggregate is defined as ORDERED.
aggsortop oid pg_operator.oid Associated sort operator OID (zero if none)
aggtranstype oid pg_type.oid Data type of the aggregate function’s internal transition (state) data