| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Dave Crooke <dcrooke(at)gmail(dot)com> |
| Cc: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Michael Glaesemann <grzm(at)seespotcode(dot)net>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Picking out the most recent row using a time stamp column |
| Date: | 2011-02-25 00:20:00 |
| Message-ID: | 4D66F5B0.5080502@agliodbs.com |
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| Lists: | pgsql-performance |
On 2/24/11 3:38 PM, Dave Crooke wrote:
> Thanks to all .... I had a tickling feeling at the back of my mind that
> there was a neater answer here. For the record, times (all from
> in-memory cached data, averaged over a bunch of runs):
>
> Dependent subquery = 117.9 seconds
> Join to temp table = 2.7 sec
> DISTINCT ON = 2.7 sec
But wait, there's more! You haven't tested the Windowing Function
solution. I'll bet it's even faster.
SELECT id_key, time_stamp, value
FROM (
SELECT id_key, time_stamp, value,
row_number()
OVER ( PARTITION BY id_key
ORDER BY time_stamp DESC)
as ranking
FROM thetable
) as filtered_table
WHERE ranking = 1
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
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