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Re: mysterious difference in speed when combining two queries with OR - Mailing list pgsql-performance

From A. Kretschmer
Subject Re: mysterious difference in speed when combining two queries with OR
Date
Msg-id 20080423085704.GG8401@a-kretschmer.de
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In response to Re: mysterious difference in speed when combining two queries with OR  ("A. Kretschmer" <andreas.kretschmer@schollglas.com>)
Responses Re: mysterious difference in speed when combining two queries with OR  (Hans Ekbrand <hans.ekbrand@sociology.gu.se>)
List pgsql-performance
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am  Wed, dem 23.04.2008, um  9:58:10 +0200 mailte A. Kretschmer folgendes:
> > Query A (two queries)
> >
> > select distinct moment.mid from moment,timecard where parent = 45 and (pid=17 and timecard.mid = moment.mid) order
bymoment.mid; 
> > select distinct moment.mid from moment,timecard where parent = 45 and (pbar = 0) order by moment.mid;
> >
> > Query B (combining the two with OR)
> >
> > select distinct moment.mid from moment,timecard where parent = 45 and ((pid=17 and timecard.mid = moment.mid) or
(pbar= 0)) order by moment.mid; 

Thanks to depesz on #postgresql (irc-channel):

Query A, the second query: there are no join between the 2 tables.
Mistake?


Andreas
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Andreas Kretschmer
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