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.
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