Re: big distinct clause vs. group by
От | Claudio Freire |
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Тема | Re: big distinct clause vs. group by |
Дата | |
Msg-id | BANLkTikOUovTjsK8_9htTjrocHJxrGUv2g@mail.gmail.com обсуждение исходный текст |
Ответ на | Re: big distinct clause vs. group by (Robert Klemme <shortcutter@googlemail.com>) |
Список | pgsql-performance |
On Tue, Apr 19, 2011 at 11:07 AM, Robert Klemme <shortcutter@googlemail.com> wrote: > I find that slightly contradictory: either you do care about the > values then your business requirements dictate the aggregate function. > If you only want to pick any value actually in the table but do not > care about which one (e.g. MIN or MAX or any other) then you don't > actually care about the value. Because "SELECT a, MAX(b) ... GROUP BY > a" and "SELECT a, MIN(b) ... GROUP BY a" are not equivalent. And, if > you do not care then there is probably no point in selecting them at > all. At best you could use a constant for any legal value then. I know it sounds weird, but there are at times when you only want one of the actual values - but don't care which one precisely. It happened to me at least once. So, it may sound as nonsense, but it is probably not. Just uncommon.
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