From: Bruno Wolff III <bruno@wolff.to>
To: Josh Berkus <josh@agliodbs.com>
Cc: Vincent-Olivier Arsenault <vincent@up4c.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: order by x DESC, y ASC indexing problem
Date: Thu, 3 Oct 2002 22:12:11 -0500
Message-ID: <20021004031211.GB3484@wolff.to> (raw)
In-Reply-To: <web-1771021@davinci.ethosmedia.com>
References: <3D9CF7EC.8080102@up4c.com>
<web-1771021@davinci.ethosmedia.com>
On Thu, Oct 03, 2002 at 19:30:59 -0700,
Josh Berkus <josh@agliodbs.com> wrote:
> Vincent,
>
> > SELECT * FROM TABLE1 ORDER BY X DESC, Y ASC;
> >
> > (X is a date and Y a varchar)
> >
> > What would that index be?
> >
> > Is there a function I can use, to invert x (the date), so that I can
> > make a query / index set like :
>
> PostgreSQL's sorting mechanism can use an index either ascending or
> descending; it does not make a difference.
Note this is referring to a multicolumn index. To use all columns of
a multicolumn index the sort directions all need to be the same.
However you are right to point out that this may not be a big deal for
many applications where using the index on the first column gets the
majority of the speed up.
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To: pgsql-sql@postgresql.org
Cc: bruno@wolff.to, josh@agliodbs.com, vincent@up4c.com
Subject: Re: order by x DESC, y ASC indexing problem
In-Reply-To: <20021004031211.GB3484@wolff.to>
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