pg_aggregate

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
agginvtransfn	regproc	pg_proc.oid	The OID in pg_proc of the inverse function of aggtransfn
aggprelimfn	regproc		Preliminary function OID (zero if none)
agginvprelimfn	regproc	pg_proc.oid	The OID in pg_proc of the inverse function of aggprelimfn
aggfinalfn	regproc	pg_proc.oid	Final function OID (zero if none)
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
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
aggordered	boolean		If true, the aggregate is defined as ORDERED.