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
.
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 (non-aggregated) arguments of an ordered-set or
hypothetical-set 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 moving-aggregate mode (zero if none) |
Inverse transition function for moving-aggregate mode (zero if none) |
Final function for moving-aggregate 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 moving-aggregate mode (zero if none) |
Approximate average size (in bytes) of the transition state data for moving-aggregate 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 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 38.12
for more information about
writing aggregate functions and the meaning of the transition
functions, etc.