postgresql 自定義aggregate function實現reduce

create or replace function lmy(first INTEGER, item INTEGER) returns INTEGER as $$
BEGIN
  return first * item;
END;
$$
LANGUAGE plpgsql;

create aggregate yml(INTEGER) (
  sfunc = lmy,
  stype = INTEGER,
  initcond = 1
);

isnp=# select i, yml(i) over (order by i) from generate_series(1,10) i;

i	yml
1	1
2	2
3	6
4	24
5	120
6	720
7	5040
8	40320
9	362880
10	3628800