[postgis-devel] Re: [HACKERS] join selectivity

[strk at refractions.net]

On Thu, Dec 23, 2004 at 10:13:03AM -0500, Tom Lane wrote:
> strk at refractions.net writes:
> > On Thu, Dec 23, 2004 at 10:01:33AM -0500, Tom Lane wrote:
> >> 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.
> 
> > Doesn't JOINSEL have access to RESTRICTSEL output for REL1 and REL2 ?
> 
> You could probably compare the fields of the RelOptInfo structures,
> but what are you going to do with it?  AFAICS you *should not* make
> the join selectivity depend on that.

So it should NOT depend on full number of rows either, is this right ?

--strk;

> 
> 			regards, tom lane
> 
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