Re: speeding up subqueries

Hi,
try to use "exists" instead of "in".

CoL

Phil Glatz wrote:
> I'm having difficulties getting a subselect to perform well.  I've used
> EXPLAIN to try to understand the problem, but can't see anything
> wrong.  I've also created appropriate indexes, but am wondering if there is
> something else involved in my particular situation.
>
> Here is my query:
>
> SELECT COUNT(*) FROM quiksearch q
> WHERE q.resource_status_id=1
> AND q.org_id IN (
> SELECT org_id FROM org_resource_type WHERE resource=12
> );
>
> Both tables are simple and small (5000 rows in quiksearch, 12000 in
> org_resource_type).
>
> q.org_id is an integer
>
> I've tried this with three values for the constant in the inner subquery
>
> n  rows in subquery  execution time
> -- ---------------   ---------------
> 12       301            3 sec
>   3      1136          182 sec
> 16      1129            7 sec
>
> The subqueries themselves all execute in less than one second.
>
> I also tried running the second subquery, saving the values in a list
> (1,2,3...), and hard coding that in instead of a subquery, execution time
> dropped to three seconds.  i.e.
>
> SELECT COUNT(*)
> FROM quiksearch q
> WHERE q.resource_status_id=1
> AND q.org_id IN (
> 9,25,512,36,3,167,166,169,170,.........
> );
>
> I don't understand what is going on here, since the inner subquery runs
> very fast, and the entire query also runs fast if I substitute the list of
> returned values instead of a subquery.
>
>
> Is there a way to make this query run faster?  Are there tricks to
> optimizing subqueries?
>
>
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