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Date: Thu, 10 Jun 2010 14:37:12 -0500
From: Kenneth Marshall <ktm@rice.edu>
To: Anne Rosset <arosset@collab.net>
Cc: Jochen Erwied <jochen@pgsql-performance.erwied.eu>,
	pgsql-performance@postgresql.org
Subject: Re: Need to increase performance of a query
Message-ID: <20100610193712.GL3063@aart.is.rice.edu>
References: <4C1125F0.8090101@collab.net> <4C112B19.6080908@krogh.cc>
	<4C113098.5040105@collab.net> <98414706.20100610212211@erwied.eu>
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On Thu, Jun 10, 2010 at 12:34:07PM -0700, Anne Rosset wrote:
> Jochen Erwied wrote:
>> Thursday, June 10, 2010, 8:36:08 PM you wrote:
>>
>>   
>>> psrdb=# (SELECT
>>> psrdb(#        MAX(item_rank.rank) AS maxRank
>>> psrdb(# FROM
>>> psrdb(#        item_rank item_rank
>>> psrdb(# WHERE
>>> psrdb(#        item_rank.project_id='proj2783'
>>> psrdb(#         AND item_rank.pf_id IS NULL
>>> psrdb(#
>>> psrdb(# )
>>> psrdb-# ORDER BY
>>> psrdb-# maxRank DESC;
>>>     
>>
>> Don't think it does really matter, but why do you sort a resultset 
>> consisting of only one row?
>>
>>   
> Sorry, I should have removed the ORDER by (the full query has a union).
> So without the ORDER by, here are the results:
> psrdb=# SELECT
> psrdb-#        MAX(item_rank.rank) AS maxRank
> psrdb-# FROM
> psrdb-#        item_rank item_rank
> psrdb-# WHERE
> psrdb-#        item_rank.pf_id='plan1408';
>   maxrank
> -------------
> 20504000000
> (1 row)
>
> Time: 1.516 ms
> psrdb=# SELECT
> psrdb-#        MAX(item_rank.rank) AS maxRank
> psrdb-# FROM
> psrdb-#        item_rank item_rank
> psrdb-# WHERE
> psrdb-#        item_rank.project_id='proj2783'
> psrdb-#         AND item_rank.pf_id IS NULL;
>   maxrank
> -------------
> 20200000000
> (1 row)
>
> Time: 13.177 ms
>
> Is there anything that can be done for the second one?
>
> Thanks,
> Anne
>
What about an IS NULL index on pf_id?

Regards,
Ken