Re: why the big difference on this explain analyze?

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От Dan Langille
Тема Re: why the big difference on this explain analyze?
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Msg-id 20020316222258.15B653F28@bast.unixathome.org
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Ответ на Re: why the big difference on this explain analyze?  (Tom Lane <tgl@sss.pgh.pa.us>)
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On 16 Mar 2002 at 17:19, Tom Lane wrote:

> "Dan Langille" <dan@langille.org> writes:
> > The difference between the two SQL statements is the inclusion of 
> > Ports_Check in the WHERE EXISTS select clause.
> 
> Which caused it to do the wrong thing.  I think you'll find this
> command set found_in_ports = TRUE in *every* row of Ports_Check.

Yes, it did.  Not quite what I want either....

> Reason: the EXISTS clause no longer depends on the outer update,
> but evaluates to a constant TRUE.  (Or possibly a constant FALSE,
> but that seems unlikely.)

Seems I'll have to keep searching for my speed improvement.  Thanks for 
pointing out that problem.  cheers.
-- 
Dan Langille
The FreeBSD Diary - http://freebsddiary.org/ - practical examples



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