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

   Column Type

   Description

   aggfnoid regproc (references 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 (references pg_proc.oid)

   Transition function

   aggfinalfn regproc (references pg_proc.oid)

   Final function (zero if none)

   aggcombinefn regproc (references pg_proc.oid)

   Combine function (zero if none)

   aggserialfn regproc (references pg_proc.oid)

   Serialization function (zero if none)

   aggdeserialfn regproc (references pg_proc.oid)

   Deserialization function (zero if none)

   aggmtransfn regproc (references pg_proc.oid)

   Forward transition function for moving-aggregate mode (zero if none)

   aggminvtransfn regproc (references pg_proc.oid)

   Inverse transition function for moving-aggregate mode (zero if none)

   aggmfinalfn regproc (references 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

   aggfinalmodify char

   Whether aggfinalfn modifies the transition state value: r if it is
   read-only, s if the aggtransfn cannot be applied after the aggfinalfn,
   or w if it writes on the value

   aggmfinalmodify char

   Like aggfinalmodify, but for the aggmfinalfn

   aggsortop oid (references pg_operator.oid)

   Associated sort operator (zero if none)

   aggtranstype oid (references 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 (references 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 36.12 for more information about writing aggregate
   functions and the meaning of the transition functions, etc.