From: Tim Landscheidt <tim@tim-landscheidt.de>
To: pgsql-sql@postgresql.org
Subject: Re: Window function sort order help
Date: Fri, 16 Sep 2011 23:55:57 +0000
Message-ID: <m3aaa4nisy.fsf@passepartout.tim-landscheidt.de> (raw)
References: <25770AAABEA9A2499B5427E0DCEE9C9B323706179A@BE262.mail.lan>
Dianna Harter <dharter@mynewplace.com> wrote:
> Having trouble getting a window function to sort correctly.
> Given this data
> consumer_id | move_date | history_timestamp
> -------------+------------+----------------------------
> 12345| 2008-01-05 | 2007-12-11 06:02:26.842171
> 12345| 2008-02-29 | 2008-02-05 07:22:38.04067
> 12345| 2008-02-29 | 2008-07-11 09:03:42.44044
> 23456| 2009-01-01 | 2008-11-12 07:33:32.656658 <--
> 23456| 2009-01-28 | 2008-11-14 01:57:40.264335
> 23456| 2009-01-01 | 2008-12-04 17:14:20.279999 <--
> 23456| 2009-01-01 | 2008-12-31 00:33:37.204968
> 23456| 2009-01-01 | 2011-06-08 04:16:41.646521
> 34567| 2010-05-07 | 2010-06-08 05:14:43.842172
> I'm trying to get the timestamp when the consumer last changed their move_date. (Notice consumer_id 23456 set their move_date to 2009-01-01 then changed and then changed it back. In the end, I want the timestamp from when they changed it to 2009-01-01 the second time.)
> My thought was to do an intermediary step to find the timestamp for each time it switched. From there I can grab the max(timestamp) for each consumer.
> [...]
> Any suggestions to get the order by to occur first then the partition by or maybe there another approach that I could use?
If I understand the question correctly, try:
| SELECT DISTINCT ON (consumer_id) consumer_id, move_date, history_timestamp
| FROM (SELECT consumer_id, move_date, history_timestamp,
| LAG(move_date) OVER (PARTITION BY consumer_id ORDER BY consumer_id, history_timestamp) AS previous_move_date
| FROM consumer_hist) AS SubQuery
| WHERE move_date IS DISTINCT FROM previous_move_date
| ORDER BY consumer_id, history_timestamp DESC;
Tim
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: tim@tim-landscheidt.de
Subject: Re: Window function sort order help
In-Reply-To: <m3aaa4nisy.fsf@passepartout.tim-landscheidt.de>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox