From: Sean Davis <sdavis2@mail.nih.gov>
To: Rick Schumeyer <rschumeyer@ieee.org>
To: pgsql-sql@postgresql.org
Subject: Re: question re. count, group by, and having
Date: Tue, 11 Oct 2005 09:07:04 -0400
Message-ID: <BF713138.10317%sdavis2@mail.nih.gov> (raw)
In-Reply-To: <000b01c5ce62$514db090$0300a8c0@dell8200>
On 10/11/05 8:50 AM, "Rick Schumeyer" <rschumeyer@ieee.org> wrote:
> The following query returns an error ("column c does not exist") in pg 8.0.3:
>
>
>
> (The column 'state' is the two letter abbreviation for a US state)
>
>
>
> -- get the number of rows for each state; list in descending order; include
> only states with at least 6 rows
>
> select state, count(state) as c from t group by state having c > 5 order by c
> desc; -- gives error
>
>
>
> If I leave the having clause out, I get the expected results:
>
>
>
> select state, count(state) as c from t group by state order by c desc; -- this
> works
>
>
>
> Is this a bug or a feature? I'm not sure why I can use 'c' in the order by
> clause but not the having clause. pg is much happier with the full "having
> count(state) > 5". Will this cause count to be evaluated twice?
I think that postgres is smart enough to do the evaluation only once, but
this might be version-dependent, but one of the gurus will have to comment
on which version (if there is a version dependence) first made this
improvement.
Sean
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To: pgsql-sql@postgresql.org
Cc: sdavis2@mail.nih.gov, rschumeyer@ieee.org
Subject: Re: question re. count, group by, and having
In-Reply-To: <BF713138.10317%sdavis2@mail.nih.gov>
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