| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Performance issues |
| Date: | 2015-03-17 14:43:00 |
| Message-ID: | 55083D74.4000601@2ndquadrant.com |
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| Lists: | pgsql-performance |
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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