Re: [GENERAL] Trouble: subquery doesn't terminate

Mel Wilson wrote:
>
> Trouble: I'm running CGI perl routines from Apache (without
> mod_perl) to query a small database. This query ran over 6 minutes
> before Apache timed out and dropped the pipe:
>
> $result = $conn->exec(qq/
> SELECT t.tune_id, t.title
> FROM tune t
> WHERE t.tune_id IN
> (SELECT c.tune_id FROM composer c WHERE c.person_id = $person_id)
> /);

The IN Clause is known to be very slow. Try to use the EXISTS clause
instead. I had the same problem. After changing to the EXISTS
variant my performance troubles went away.
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Herbert Liechti E-Mail: Herbert(dot)Liechti(at)thinx(dot)ch
ThinX networked business services Stahlrain 10, CH-5200 Brugg
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~