Re: big distinct clause vs. group by

Поиск
Список
Период
Сортировка
От Claudio Freire
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.

В списке pgsql-performance по дате отправления:

Предыдущее
От: Laurent Laborde
Дата:
Сообщение: postgresql random io test with 2 SSD Kingston V+100 500GB in (software) Raid1
Следующее
От: Laurent Laborde
Дата:
Сообщение: Re: postgresql random io test with 2 SSD Kingston V+100 500GB in (software) Raid1