Date: Thu, 16 Dec 2004 11:41:54 +0100
To: pgsql-sql@postgresql.org
Subject: question about index
Message-ID: <20041216104154.GA30578@mail.librelogiciel.com>
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From: Jerome Alet <alet@librelogiciel.com>

Hi,

For a future databas, I plan to have got a table with a text field 
which can contain only three different values, say "VALUE1", 
"VALUE2", and "VALUE3" 

this table may have, over the course of one year, several million
rows for a size around 2 Gb or more.

I'd be interested in having :

        SELECT count(*) AS nbvalue1 FROM mytable WHERE myfield='VALUE1';
        SELECT count(*) AS nbvalue2 FROM mytable WHERE myfield='VALUE2';
        SELECT count(*) AS nbvalue3 FROM mytable WHERE myfield='VALUE3';
        
be as fast as possible.        

considering that almost 70% of the rows will be with 'VALUE1', 20%
will be with 'VALUE2' and 10% will be with 'VALUE3' on the average.

should I create an index to speedup the counts or not ?

any idea of the impact of running these three queries every 5 minutes
on say 10 000 000 rows ?

thanks in advance

Jerome Alet