From: | Dimitri Fontaine <dfontaine(at)hi-media(dot)com> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Zotov <zotov(at)oe-it(dot)ru>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Query optimization problem |
Date: | 2010-07-28 11:31:39 |
Message-ID: | 871vanlu5g.fsf@hi-media-techno.com |
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Thread: | |
Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> SELECT d1.ID, d2.ID
> FROM DocPrimary d1
> JOIN DocPrimary d2 ON d2.BasedOn=d1.ID
> WHERE (d1.ID=234409763) or (d2.ID=234409763)
>
> ...you're going to scan d1, scan d2, and then join the results. The
> scan of d1 is going to produce different results depending on whether
> you evaluate or not d1.ID=234409763, and the scan of d2 is going to
> produce different results depending on whether or not you evaluate
> d2.BasedOn=234409763.
Well I just realised you can't use d2.BasedOn in scanning d1 here. I
don't know what exactly I had in mind previously, but in any case, sorry
for the noise.
I hope the optimiser effort control still hold water nonetheless…
--
dim
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