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
| Name | Type | References | Description |
|---|---|---|---|
aggfnoid | regproc | | 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 | | Transition function |
aggfinalfn | regproc | | Final function (zero if none) |
aggcombinefn | regproc | | Combine function (zero if none) |
aggserialfn | regproc | | Serialization function (zero if none) |
aggdeserialfn | regproc | | Deserialization function (zero if none) |
aggmtransfn | regproc | | Forward transition function for moving-aggregate mode (zero if none) |
aggminvtransfn | regproc | | Inverse transition function for moving-aggregate mode (zero if none) |
aggmfinalfn | regproc | | 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 | | Associated sort operator (zero if none) |
aggtranstype | 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 | | 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 38.11 for more information about writing aggregate functions and the meaning of the transition functions, etc.