The pg_aggregate
table 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.
column  type  references  description 

aggfnoid 
regproc  pg_proc.oid  Aggregate function OID 
aggtransfn 
regproc  pg_proc.oid  Transition function OID 
aggprelimfn 
regproc  Preliminary function OID (zero if none)  
aggfinalfn 
regproc  pg_proc.oid  Final function OID (zero if none) 
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  
agginvtransfn 
regproc  pg_proc.oid  The OID in pg_proc of the inverse function of aggtransfn 
agginvprelimfn 
regproc  pg_proc.oid  The OID in pg_proc of the inverse function of aggprelimfn 
aggordered 
Boolean  If true , the aggregate is defined as ORDERED . 

aggsortop 
oid  pg_operator.oid  Associated sort operator OID (zero if none) 
aggtranstype 
oid  pg_type.oid  Data type of the aggregate function's internal transition (state) data 
Parent topic: System Catalogs Definitions