Two Index Questions - Mailing list pgsql-sql

From Josh Berkus
Subject Two Index Questions
Date
Msg-id 200207190933.59283.josh@agliodbs.com
Whole thread Raw
Responses Re: Two Index Questions  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: Two Index Questions  (Bruno Wolff III <bruno@wolff.to>)
List pgsql-sql
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 t1GROUP BY t1.A, t1.B, t1.C
Thenwould a multi-column index on A, B, C be faster than seperate indexes  
on A, B and C?   I've run a few tests, but I don't have enough data in the
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
for DESC alpha sorts.   Has this been resolved?  If so, does one need to
create any special indexes to take advantage of indexes for DESC sorts?

Thanks for your help!

--
-Josh BerkusAglio Database SolutionsSan Francisco



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