Re: Set returning aggregate?

No, final function cannot returns set. It is disallowed.

Theoretically, it should be possible - it is explicitly prohibited. But if it will be allowed, you can get same problems like using SRF function in target list.

postgres=# select generate_series(1,2),generate_series(1,2);
 generate_series │ generate_series
─────────────────┼─────────────────
               1 │               1
               2 │               2
(2 rows)

Time: 49.332 ms
postgres=# select generate_series(1,2),generate_series(1,3);
 generate_series │ generate_series
─────────────────┼─────────────────
               1 │               1
               2 │               2
               1 │               3
               2 │               1
               1 │               2
               2 │               3
(6 rows)

Time: 0.445 ms

It will be hard defined a expected behaviour when somebody use more these aggregates in same query and returns different number of rows.

Regards

Pavel