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48.2. 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 48-2. pg_aggregate Columns

Name Type References Description
aggfnoid regproc pg_proc.oid pg_proc 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
aggfinalfn regproc pg_proc.oid Final function (zero if none)
aggmtransfn regproc pg_proc.oid Forward transition function for moving-aggregate mode (zero if none)
aggminvtransfn regproc pg_proc.oid Inverse transition function for moving-aggregate mode (zero if none)
aggmfinalfn regproc pg_proc.oid Final function 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 (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.

New aggregate functions are registered with the CREATE AGGREGATE command. See Section 35.10 for more information about writing aggregate functions and the meaning of the transition functions, etc.

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