pg_aggregate
| PostgreSQL 9.2.20 Documentation | ||||
|---|---|---|---|---|
| Prev | Up | Chapter 45. 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 45-2. pg_aggregate Columns
| Name | Type | References | Description |
|---|---|---|---|
| aggfnoid | regproc | pg_proc .oid | pg_proc OID of the aggregate function |
| aggtransfn | regproc | pg_proc .oid | Transition function |
| aggfinalfn | regproc | pg_proc .oid | Final function (zero if none) |
| 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 |
| 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. |
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.