Re: [HACKERS] psql nested queries with 2000+ records

OK, I think I see the problem. Indexes are not being used in this case.
Basically for every row in the outer query, you are doing a sequential
scan in the inner table.

Can you try this:

select * into games2 from games;
explain select name from games where name in (select name from games2 where
name like 'A%');

I would like to know if the use of the same table in the subquery is
causing the problem. I assume you have run vacuum and vacuum analyze.

>
> At 12:24 PM 3/20/98 -0500, Bruce Momjian wrote:
>
> >Very strange. 15+ minutes? Wow, that is terrible, even longer than a
> >sequential scan of the table. Try EXPLAIN and tell us what it says in
> >the two cases.
>
> This is within the 2717 record database.
>
> explain select name from games where name in (select name from games where
> name like 'A%');
>
> NOTICE: QUERY PLAN:
>
> Seq Scan on games (cost=207.95 size=446 width=12)
> SubPlan
> -> Seq Scan on games (cost=207.95 size=1 width=12)
>
> NOTICE: QUERY PLAN:
>
> Seq Scan on games (cost=207.95 size=446 width=12)
> SubPlan
> -> Seq Scan on games (cost=207.95 size=1 width=12)
>
> EXPLAIN
>
> This is within the 24 record database of the same type of data
>
> explain select name from games where name in (select name from game
> s where name like 'A%');
> NOTICE: QUERY PLAN:
>
> Seq Scan on games (cost=207.95 size=446 width=12)
> SubPlan
> -> Seq Scan on games (cost=207.95 size=1 width=12)
>
> NOTICE: QUERY PLAN:
>
> Seq Scan on games (cost=207.95 size=446 width=12)
> SubPlan
> -> Seq Scan on games (cost=207.95 size=1 width=12)
>
> EXPLAIN
>
> Obviously, I get the same information, any suggestions?
>
> -Coronach(at)hill-b-073(dot)resnet(dot)purdue(dot)edu
>
>

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