Re: Optimizer & boolean syntax - Mailing list pgsql-hackers

From scott.marlowe
Subject Re: Optimizer & boolean syntax
Date
Msg-id Pine.LNX.4.33.0211211558530.23988-100000@css120.ihs.com
Whole thread Raw
In response to Re: Optimizer & boolean syntax  ("Christopher Kings-Lynne" <chriskl@familyhealth.com.au>)
List pgsql-hackers
On Thu, 21 Nov 2002, Christopher Kings-Lynne wrote:

> > > I think his point is that they _should_ be equivalent.  Surely there's
> > > something in the optimiser that discards '=true' stuff, like 'a=a'
> should be
> > > discarded?
> >
> > I figure that's what he meant, but it isn't what was said. ;)
> >
> > "col" isn't of the general form "indexkey op constant" or "constant op
> > indexkey" which I presume it's looking for given the comments in
> > indxpath.c.  I'm not sure what the best way to make it work would be given
> > that presumably we'd want to make col IS TRUE/FALSE use an index at the
> > same time (since that appears to not do so as well).
> 
> Not that I see the point of indexing booleans, but hey :)

While full indexes do seem futile, partial indexes can be quite useful.

select articles from forum where approved is false

if 99.9% of all articles are approved would be quite common.



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