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
`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