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Re: index suggestion for 7.4

From: Bruno Wolff III <bruno(at)wolff(dot)to>
To: Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: index suggestion for 7.4
Date: 2003-05-30 18:02:13
Message-ID: 20030530180213.GA23374@wolff.to (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, May 30, 2003 at 10:42:24 -0700,
  Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com> wrote:
> On Fri, 30 May 2003, Bruno Wolff III wrote:
> 
> > Now that expressions can be used in indexes in 7.4 you can have multicolumn
> > indexes that are ordered in different directions. However the planner
> > doesn't seem to understand that order by -col asc is the same as order by
> > col desc (for at least the normal -) so you have to be careful how you
> > write queries when doing this.
> 
> I think it'd be better to make it easier to make indexes where some
> columns are reversed.  I'm not sure that making a reverse opclass for
> btree (one that goes >, >=, =, <=, < I guess) is a complete solution
> even for btree but if it is, we could provide them.  I think this would
> also have the advantage of not requiring wacky queries to use the index
> for multicolumn lookups as well.

I was hoping the new stuff Tom added would make doing this easier. The issue
has come up before and at least at that time it didn't get changed so I
expected it wasn't easy to do.

I thought maybe there was information for the - operator
that would allow you to know that you could use an index on -col
to go in the reverse direction safely.

The new stuff still is easier to use then creating a new opclass which was
the old solution.

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