2009/7/17 Pavel Stehule <pavel.stehule@gmail.com>:
> Hello
>
> look on:
> postgres=# explain select count(*) over () from x;
> QUERY PLAN
> -------------------------------------------------------------
> WindowAgg (cost=0.00..265.00 rows=10000 width=0)
> -> Seq Scan on 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
Well, how about "select a from x order by a"?
I wonder if index scan affects more than windowagg.
--
Hitoshi Harada