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Re: Using index from sub-query

From: "Mike Mascari" <mascarm(at)mascari(dot)com>
To: "pdaly" <petedaly(at)ix(dot)netcom(dot)com>, <pgsql-general(at)postgresql(dot)org>
Subject: Re: Using index from sub-query
Date: 2000-08-28 15:48:24
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Lists: pgsql-general
> From: pdaly <petedaly(at)ix(dot)netcom(dot)com>
> As has been talked about recently, I have a int8 field, which when
searched for
> as 'value' will use the index, but as value, with the quotes will not.
> I subquery to get a list of the values to look up:
> SELECT [fields]
>      FROM table1
>      WHERE id in (
>         select distinct id from namelookup where name = '$tname'
>         )
> When I do an explain on this, it is doing a table scan, and not using the
> table1.  It will only use the index when the value to be matched is in
> How can I force it to use the index, or create a new index which would be
> This causes a HUGE performance hit.  (30-45 seconds, as opposed to less
than 1
> second.)

Unfortunately, PostgreSQL doesn't use indexes with IN clauses. 
Its on the list of things TODO though. At the moment, you have
to write the query using EXISTS instead:

SELECT table1.[fields] FROM table1
(SELECT FROM namelookup WHERE = AND name = '$tname');

Hope that helps,

Mike Mascari

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