Date: Thu, 1 Jun 2006 09:53:10 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Miroslav ?ulc <miroslav.sulc@startnet.cz>
Cc: pgsql-sql@postgresql.org
Subject: Re: SELECT DISTINCT too slow
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	pgsql-sql@postgresql.org
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Miroslav ?ulc wrote:
> Hello,
> 
> I have a table with cca 400,000 rows. The table contains column "key" of
> varchar(20) type containing 10 distinct values. I want to get out what
> distinct values are present in the column. I use this simple query,
> which is very slow:
> 
> SELECT DISTINCT Key FROM MRTPContactValue

You could get the universe of values from the table where this is a
primary key, and use an IN clause (which apparently is more efficient
than an EXISTS in some cases, but try that too) to search for values
that exist in the MRTPContactValue table.

I assume you do have the other table, don't you?

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.