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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