---
title: "pg_aggregate"
id: catalog-pg-aggregate
pg_version: "20devel"
---

<a id="catalog-pg-aggregate"></a>

## 52.2. 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](catalog-pg-proc.md). The pg_proc entry carries the aggregate's name, input and output data types, and other information that is similar to ordinary functions. 

**pg_aggregate Columns**

| Column Type | Description | 
| --- | --- |
| `aggfnoid` `regproc` (references [pg_proc](catalog-pg-proc.md).`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` (references [pg_proc](catalog-pg-proc.md).`oid`) | Transition function |
| `aggfinalfn` `regproc` (references [pg_proc](catalog-pg-proc.md).`oid`) | Final function (zero if none) |
| `aggcombinefn` `regproc` (references [pg_proc](catalog-pg-proc.md).`oid`) | Combine function (zero if none) |
| `aggserialfn` `regproc` (references [pg_proc](catalog-pg-proc.md).`oid`) | Serialization function (zero if none) |
| `aggdeserialfn` `regproc` (references [pg_proc](catalog-pg-proc.md).`oid`) | Deserialization function (zero if none) |
| `aggmtransfn` `regproc` (references [pg_proc](catalog-pg-proc.md).`oid`) | Forward transition function for moving-aggregate mode (zero if none) |
| `aggminvtransfn` `regproc` (references [pg_proc](catalog-pg-proc.md).`oid`) | Inverse transition function for moving-aggregate mode (zero if none) |
| `aggmfinalfn` `regproc` (references [pg_proc](catalog-pg-proc.md).`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` |
| `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` (references [pg_operator](catalog-pg-operator.md).`oid`) | Associated sort operator (zero if none) |
| `aggtranstype` `oid` (references [pg_type](catalog-pg-type.md).`oid`) | Data type of the aggregate function's internal transition (state) data |
| `aggtransspace` `int4` | Approximate average size (in bytes) of the transition state data. A positive value provides an estimate; zero means to use a default estimate. A negative value indicates the state data can grow unboundedly in size, such as when the aggregate accumulates input rows (e.g., array_agg, string_agg). |
| `aggmtranstype` `oid` (references [pg_type](catalog-pg-type.md).`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`](sql-createaggregate.md) command. See [Section 36.12](xaggr.md) for more information about writing aggregate functions and the meaning of the transition functions, etc.