Pass extra parameter to PostgreSQL aggregate final function

Question

Is the only way to pass an extra parameter to the final function of a PostgreSQL aggregate to create a special TYPE for the state value?

e.g.:

CREATE         


        

Answer 1

You can define an aggregate with more than one parameter.

I don't know if that solves your problem, but you could use it like this:

CREATE OR REPLACE FUNCTION myaggsfunc(integer, integer, text) RETURNS integer
   IMMUTABLE STRICT LANGUAGE sql AS
$f$
   SELECT CASE $3
           WHEN '+' THEN $1 + $2
           WHEN '*' THEN $1 * $2
           ELSE NULL
        END
$f$;

CREATE AGGREGATE myagg(integer, text) (
   SFUNC = myaggsfunc(integer, integer, text),
   STYPE = integer
);

It could be used like this:

CREATE TABLE mytab
   AS SELECT * FROM generate_series(1, 10) i;

SELECT myagg(i, '+') FROM mytab;

 myagg 
-------
    55
(1 row)

SELECT myagg(i, '*') FROM mytab;

  myagg  
---------
 3628800
(1 row)