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
Column Type Description 


Aggregate kind: 
Number of direct (nonaggregated) arguments of an orderedset or hypotheticalset aggregate, counting a variadic array as one argument. If equal to 
Transition function 
Final function (zero if none) 
Combine function (zero if none) 
Serialization function (zero if none) 
Deserialization function (zero if none) 
Forward transition function for movingaggregate mode (zero if none) 
Inverse transition function for movingaggregate mode (zero if none) 
Final function for movingaggregate mode (zero if none) 
True to pass extra dummy arguments to 
True to pass extra dummy arguments to 
Whether 
Like 
Associated sort operator (zero if none) 
Data type of the aggregate function's internal transition (state) data 
Approximate average size (in bytes) of the transition state data, or zero to use a default estimate 
Data type of the aggregate function's internal transition (state) data for movingaggregate mode (zero if none) 
Approximate average size (in bytes) of the transition state data for movingaggregate mode, or zero to use a default estimate 
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. 
The initial value of the transition state for movingaggregate 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 38.12 for more information about writing aggregate functions and the meaning of the transition functions, etc.
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