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From: "Josh Berkus" <josh@agliodbs.com>
Subject: Re: order by x DESC, y ASC indexing problem
To: Vincent-Olivier Arsenault <vincent@up4c.com>,
	pgsql-sql@postgresql.org
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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.

However, most of the time ORDER BY does not use an index at all because
a seq scan is faster.   Usually, ORDER BY  uses an index only when
combined with related criteria and/or the LIMIT clause.

-Josh Berkus