pg_aggregate

PostgreSQL 7.2 Documentation
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# 3.2. pg_aggregate

`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`.

Table 3-2. pg_aggregate Columns

Name | Type | References | Description
--- | --- | --- | ---
aggname | `name` |  | Name of the aggregate function
aggowner | `int4` | pg_shadow.usesysid | Owner (creator) of the aggregate function
aggtransfn | `regproc` (function) | pg_proc.oid | Transition function
aggfinalfn | `regproc` (function) | pg_proc.oid | Final function
aggbasetype | `oid` | pg_type.oid | The input datatype for this aggregate function
aggtranstype | `oid` | pg_type.oid | The type of the aggregate function's internal transition (state) data
aggfinaltype | `oid` | pg_type.oid | The type of the result
agginitval | `text` |  | The initial value of the transition state. This is a text field containing the initial value in its external string representation. If the field is NULL, the transition state value starts out NULL.

New aggregate functions are registered with the CREATE AGGREGATE command. See the Programmer's Guide for more information about writing aggregate functions and the meaning of the transition functions, etc.

An aggregate function is identified through name and argument type. Hence aggname and aggbasetype are the composite primary key.

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