pg_aggregate
| PostgreSQL 9.6.10 Documentation | |||
|---|---|---|---|
| Prev | Up | Chapter 50. System Catalogs | Next |
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 50-2. 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) |
| aggcombinefn | regproc | pg_proc .oid | Combine function (zero if none) |
| aggserialfn | regproc | pg_proc .oid | Serialization function (zero if none) |
| aggdeserialfn | regproc | pg_proc .oid | Deserialization 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 36.10 for more information about writing aggregate functions and the meaning of the transition functions, etc.