Subject: Re: Query much faster with enable_seqscan=0 
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From: Ogden <lists@darkstatic.com>
In-Reply-To: <11723.1285111832@sss.pgh.pa.us>
Date: Tue, 12 Oct 2010 19:23:24 -0500
Cc: pgsql-performance@postgresql.org
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References: <0D5B9ED0-00C3-4EEB-8336-0B2F8A884620@darkstatic.com>
	<11723.1285111832@sss.pgh.pa.us>
To: Tom Lane <tgl@sss.pgh.pa.us>


On Sep 21, 2010, at 6:30 PM, Tom Lane wrote:

> Ogden <lists@darkstatic.com> writes:
>> SELECT tr.id, tr.sid
>>            FROM
>>            test_registration tr,
>>            INNER JOIN test_registration_result r on (tr.id =3D =
r.test_registration_id)
>>            WHERE.
>>            =
tr.test_administration_id=3D'32a22b12-aa21-11df-a606-96551e8f4e4c'::uuid
>>            GROUP BY tr.id, tr.sid
>=20
> Seeing that tr.id is a primary key, I think you might be a lot better
> off if you avoided the inner join and group by.  I think what you =
really
> want here is something like
>=20
> SELECT tr.id, tr.sid
>            FROM
>            test_registration tr
>            WHERE
>            =
tr.test_administration_id=3D'32a22b12-aa21-11df-a606-96551e8f4e4c'::uuid
>            AND EXISTS(SELECT 1 FROM test_registration_result r
>                       WHERE tr.id =3D r.test_registration_id)
>=20
> 			regards, tom lane
>=20

Thank you for this suggestion, however, what if I wanted some columns =
from test_registration_result - this wouldn't work, for example if I =
wanted test_registration_result.answer to be fetched. Hence, I had to =
have a JOIN with test_registration_result and a GROUP BY. I still am not =
happy with my query - the EXISTS executes in great speed however I =
cannot retrieve any of the columns from that table.=20

Thank you

Ogden