Re: [GENERAL] Query is not using index when it should

From: Steinar H. Gunderson
Subject: Re: [GENERAL] Query is not using index when it should
Date: ,
Msg-id: 20041211143213.GA2659@uio.no
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In response to: Re: [GENERAL] Query is not using index when it should  ( (Tomas Skäre))
Responses: Re: [GENERAL] Query is not using index when it should  (Michael Fuhr)
Re: [GENERAL] Query is not using index when it should  ( (Tomas Skäre))
List: pgsql-performance

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Re: [GENERAL] Query is not using index when it should  (Stephan Szabo, )
 Re: [GENERAL] Query is not using index when it should  ( (Tomas Skäre), )
  Re: [GENERAL] Query is not using index when it should  ("Steinar H. Gunderson", )
   Re: [GENERAL] Query is not using index when it should  (Michael Fuhr, )
   Re: [GENERAL] Query is not using index when it should  ( (Tomas Skäre), )

On Sat, Dec 11, 2004 at 03:17:13PM +0100, Tomas Skäre wrote:
> select c.* from cjm_object c
>  inner join
>   (select max(timestamp) as timestamp,objectid,field from cjm_object
>    group by objectid,field) t
>   using(timestamp,objectid,field)
>  where 1=1 and data is not null
>  order by objectid,field;

Usually, SELECT max(field) FROM table is better written in PostgreSQL as
SELECT field FROM table ORDER field DESC LIMIT 1.

I don't see the point of "where 1=1", though...

/* Steinar */
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Homepage: http://www.sesse.net/


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From: Tom Lane
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Subject: Re: LIMIT causes SEQSCAN in subselect
From: tomas@nocrew.org (Tomas Skäre)
Date:
Subject: Re: [GENERAL] Query is not using index when it should