System Catalogs Definitions - pg_aggregate - 《Greenplum Database v6.23 Documentation》

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.

column	type	references	description
`aggfnoid`	regproc	pg_proc.oid	OID of the aggregate function
`aggkind`	char		Aggregate kind: `n` for normal aggregates, `o` for ordered-set aggregates, or `h` for hypothetical-set aggregates
`aggnumdirectargs`	int2		Number of direct (non-aggregated) arguments of an ordered-set or hypothetical-set aggregate, counting a variadic array as one argument. If equal to `pronargs`, the aggregate must be variadic and the variadic array describes the aggregated arguments as well as the final direct arguments. Always zero for normal aggregates.
`aggtransfn`	regproc	pg_proc.oid	Transition function OID
`aggfinalfn`	regproc	pg_proc.oid	Final function OID (zero if none)
`aggcombinefn`	regproc	pg_proc.oid	Combine function OID (zero if none)
`aggserialfn`	regproc	pg_proc.oid	OID of the serialization function to convert transtype to `bytea` (zero if none)
`aggdeserialfn`	regproc	pg_proc.oid	OID of the deserialization function to convert `bytea` to transtype (zero if none)
`aggmtransfn`	regproc	pg_proc.oid	Forward transition function OID for moving-aggregate mode (zero if none)
`aggminvtransfn`	regproc	pg_proc.oid	Inverse transition function OID for moving-aggregate mode (zero if none)
`aggmfinalfn`	regproc	pg_proc.oid	Final function OID for moving-aggregate mode (zero if none)
`aggfinalextra`	bool		True to pass extra dummy arguments to `aggfinalfn`
`aggmfinalextra`	bool		True to pass extra dummy arguments to `aggmfinalfn`
`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
`aggtransspace`	int4		Approximate average size (in bytes) of the transition state data, or zero to use a default estimate
`aggmtranstype`	oid	pg_type.oid	Data type of the aggregate function’s internal transition (state) data for moving-aggregate mode (zero if none)
`aggmtransspace`	int4		Approximate average size (in bytes) of the transition state data for moving-aggregate mode, or zero to use a default estimate
`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.
`aggminitval`	text		The initial value of the transition state for moving- aggregate mode. 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.

Parent topic: System Catalogs Definitions