Multi-column index not used, new flipped column index is

From: <ogjunk-pgjedan(at)yahoo(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: Multi-column index not used, new flipped column index is
Date: 2006-05-10 16:21:43
Message-ID: 20060510162143.96628.qmail@web50306.mail.yahoo.com
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Hi,

I'm using PG 8.0.3 and recently spotted a query that was not using a multi-column index I had created.
The index looks like:

CREATE INDEX ..... ON FooTable(fkColumnOne, fkColumnTwo);

The query that was not using the index was using:

SELECT .... a bunch of columns and joins .... WHERE FooTable.fkColumnTwo=1000;

So I added another index where the indexed columns are flipped:

CREATE INDEX ..... ON FooTable(fkColumnTwo, fkColumnOne);

Now the query started to use that index -- gooooood!
But now I have 2 indices that are nearly the same, and that means overhead during INSERTs/DELETEs. :(

Is there a way to get this to use that first index, so I don't have to have this additional index?
If I had PG 8.1.3, would PG know how to use that first index? I seem to recall something about this somewhere... but I don't see it at http://www.postgresql.org/docs/whatsnew .

Thanks,
Otis

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