| From: | "A(dot) Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com> |
|---|---|
| To: | pgsql-novice(at)postgresql(dot)org |
| Subject: | Re: using column alias to make operations |
| Date: | 2008-01-23 10:12:59 |
| Message-ID: | 20080123101259.GE20579@a-kretschmer.de |
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| Lists: | pgsql-novice |
am Wed, dem 23.01.2008, um 10:53:51 +0100 mailte Raimon Fernandez folgendes:
>
> On 23/01/2008, at 10:36, A. Kretschmer wrote:
>
> >am Wed, dem 23.01.2008, um 9:10:09 +0100 mailte Raimon Fernandez
> >folgendes:
> >>I thought I could use the column alias, because in the ORDER BY
> >>clausule I can use them ...
> >
> >You can't, because first PG fetch the result, this result has the
> >column-aliases. A consecutively ORDER BY can access this aliases,
> >but not
> >the SELECT self.
>
> ok, thanks
>
> and PG knows that there are two identical operations, and just do it
> once and use that value, or does it twice ?
Yes, of course, the former.
Andreas
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Andreas Kretschmer
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