Re: slow query using sub select

> -----Original Message-----
> From: Tim Jones [mailto:TJones@optio.com]
> Sent: Tuesday, May 23, 2006 12:11 AM
> To: pgsql-performance@postgresql.org
> Subject: [PERFORM] slow query using sub select
>
> Hi,
>   I am having a problem with a sub select query being kinda slow.  The
> query is as follows:
>
> select batterycode, batterydescription, observationdate from Battery t1
> where patientidentifier=611802158 and observationdate = (select
> max(observationdate) from Battery t2 where t2.batterycode=t1.batterycode
> and patientidentifier=611802158) order by batterydescription.


How about changing it into a standard join:


select t1.batterycode, t1.batterydescription, t2.observationdate
from Battery t1,
(Select batterycode ,max(observationdate) from Battery t2 where
patientidentifier=611802158 group by batterycode) AS T2
where t1. batterycode = t2. batterycode

Jonathan Blitz
AnyKey Limited
Israel

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