| From: | strk(at)refractions(dot)net |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Mark Cave-Ayland <m(dot)cave-ayland(at)webbased(dot)co(dot)uk>, pgsql-hackers(at)postgresql(dot)org, postgis-devel(at)postgis(dot)refractions(dot)net |
| Subject: | Re: join selectivity |
| Date: | 2004-12-23 15:10:03 |
| Message-ID: | 20041223151003.GA4535@freek.keybit.net |
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| Lists: | pgsql-hackers |
On Thu, Dec 23, 2004 at 10:01:33AM -0500, Tom Lane wrote:
> strk(at)refractions(dot)net writes:
> > Doing some tests I've found out that the returned value from the
> > JOINSEL is applied to REL1.rows X REL2.rows, but REL1 and REL2
> > are not 'base' table, rather relations with a number of
> > rows once again estimated by other selectivity functions.
>
> Right. This amounts to assuming that the join conditions and the
> restriction conditions are independent, which of course is bogus,
> but we really don't have enough information to do better.
>
> regards, tom lane
Doesn't JOINSEL have access to RESTRICTSEL output for REL1 and REL2 ?
--strk;
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