Hello
look on:
postgres=# explain select count(*) over () from x; QUERY PLAN
-------------------------------------------------------------WindowAgg (cost=0.00..265.00 rows=10000 width=0) -> Seq
Scanon x (cost=0.00..140.00 rows=10000 width=0)
(2 rows)
Time: 1,473 ms
postgres=# explain select count(*) over (order by a) from x; QUERY PLAN
------------------------------------------------------------------------WindowAgg (cost=0.00..556.25 rows=10000
width=4) -> Index Scan using gg on x (cost=0.00..406.25 rows=10000 width=4)
(2 rows)
but
query1: 160ms
query2: 72ms
regards
Pavel Stehule