Re: Picking out the most recent row using a time stamp column - Mailing list 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