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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: pgsql-performance@postgresql.org
Subject: Re: Performance issues
Date: Tue, 17 Mar 2015 15:43:00 +0100
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On 17.3.2015 15:19, Thomas Kellerer wrote:
> Tomas Vondra schrieb am 17.03.2015 um 14:55:
>>  (2) using window functions, e.g. like this:
>>
>>      SELECT * FROM (
>>        SELECT *,
>>             ROW_NUMBER() OVER (PARTITION BY touchpoint_execution_id
>>                                ORDER BY FROM max_creation_dt) AS rn
>>        FROM s_f_touchpoint_execution_status_history
>>      ) foo WHERE rn = 1
>>
>>      But estimating this is also rather difficult ...
> 
> 
> From my experience rewriting something like the above using DISTINCT 
> ON is usually faster.

How do you get the last record (with respect to a timestamp column)
using a DISTINCT ON?


-- 
Tomas Vondra                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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