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From: Josh Berkus <josh@agliodbs.com>
Reply-To: josh@agliodbs.com
Organization: Aglio Database Solutions
To: pgsql-sql@postgresql.org
Subject: Two Index Questions
Date: Fri, 19 Jul 2002 09:33:59 -0700
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Folks (esp. Tom, Stephan, and Bruce):

I have two questions for my "Adventures in PostgreSQL" article reasearch:

Multi-Column Indexes and GROUP BY:
Q:  If you group a table by multiple colums, e.g.
	SELECT t1.A, t1.B, t1.C, MAX(t1.G)
	FROM t1
	GROUP BY t1.A, t1.B, t1.C
  Then would a multi-column index on A, B, C be faster than seperate indexe=
s=20
on A, B and C?   I've run a few tests, but I don't have enough data in the=
=20
seperate tables to really get a feel for the difference.

DESC Alpha Sort Indexes:
Q: In PostgreSQL 7.0, there was an issue that indexes where never consulted=
=20
for DESC alpha sorts.   Has this been resolved?  If so, does one need to=20
create any special indexes to take advantage of indexes for DESC sorts?

Thanks for your help!

--=20
-Josh Berkus
 Aglio Database Solutions
 San Francisco