52.2. pg_aggregate

The catalog pg_aggregate 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 52.2. pg_aggregate Columns

NameTypeReferencesDescription
aggfnoidregprocpg_proc.oidpg_proc OID of the aggregate function
aggkindchar Aggregate kind: n for normal aggregates, o for ordered-set aggregates, or h for hypothetical-set aggregates
aggnumdirectargsint2 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.
aggtransfnregprocpg_proc.oidTransition function
aggcollectfnregprocpg_proc.oidCollection function (Only for Postgres-XL>)
aggfinalfnregprocpg_proc.oidFinal function (zero if none)
aggcombinefnregprocpg_proc.oidCombine function (zero if none)
aggserialfnregprocpg_proc.oidSerialization function (zero if none)
aggdeserialfnregprocpg_proc.oidDeserialization function (zero if none)
aggmtransfnregprocpg_proc.oidForward transition function for moving-aggregate mode (zero if none)
aggminvtransfnregprocpg_proc.oidInverse transition function for moving-aggregate mode (zero if none)
aggmfinalfnregprocpg_proc.oidFinal function for moving-aggregate mode (zero if none)
aggfinalextrabool True to pass extra dummy arguments to aggfinalfn
aggmfinalextrabool True to pass extra dummy arguments to aggmfinalfn
aggsortopoidpg_operator.oidAssociated sort operator (zero if none)
aggtranstypeoidpg_type.oidData type of the aggregate function's internal transition and collection (state) data (Revised for Postgres-XL)
aggtransspaceint4 Approximate average size (in bytes) of the transition state data, or zero to use a default estimate
aggmtranstypeoidpg_type.oidData type of the aggregate function's internal transition (state) data for moving-aggregate mode (zero if none)
aggmtransspaceint4 Approximate average size (in bytes) of the transition state data for moving-aggregate mode, or zero to use a default estimate
agginitvaltext  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.
agginitcollecttext  The initial value of the collection state. This is a text field containing the initial value in its external string representation. If this field is null, the collection state value starts out null. (Only for Postgres-XL)
aggminitvaltext  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.

New aggregate functions are registered with the CREATE AGGREGATE command. See Section 37.10 for more information about writing aggregate functions and the meaning of the transition functions, etc.