Re: group by will not use an index?
От
Steinar H. Gunderson
Тема
Re: group by will not use an index?
Дата
Msg-id
20070110011104.GA21351@uio.no
Ответ на
Re: group by will not use an index? (Brian Herlihy)
Список
Дерево обсуждения
group by will not use an index? tsuraan <tsuraan@gmail.com>
Re: group by will not use an index? "Adam Rich" <adam.r@sbcglobal.net>
Re: group by will not use an index? Scott Marlowe <smarlowe@g2switchworks.com>
Re: group by will not use an index? Andrew Lazarus <andrew@pillette.com>
Re: group by will not use an index? tsuraan <tsuraan@gmail.com>
On Tue, Jan 09, 2007 at 05:07:03PM -0800, Brian Herlihy wrote: > Actually, as I recently discovered, GROUP BY is faster than DISTINCT. It's > just due to how they are implemented, so don't go looking for any deep > reason :) The thread "GROUP BY vs DISTINCT" from 2006-12-20 discusses it. > DISTINCT sorts the results to find the unique rows, but GROUP BY uses a > hash. Actually, GROUP BY _can_ use a sort too, it's just that a hash is usually faster. /* Steinar */ -- Homepage: http://www.sesse.net/
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