I think because you are not selecting the column you are referring to.
Try:
HAVING SUM(y)>3
Kris
On 25-Nov-09, at 14:20, Rikard Bosnjakovic
<rikard.bosnjakovic@gmail.com> wrote:
> (Postgres version 8.2.4)
>
> Trying to understand GROUP BY, I'm reading on
> <http://www.postgresql.org/docs/8.4/interactive/queries-table-expressions.html
> >.
> Consider this query:
>
> => select x, sum(y) from test1 group by x order by x;
> x | sum
> ---+-----
> a | 4
> b | 5
> c | 2
> (3 rows)
>
> I understand what's happening here, all is fine. So I play with
> HAVING:
>
> => select x, sum(y) from test1 group by x having sum(y)>3 order by x;
> x | sum
> ---+-----
> a | 4
> b | 5
> (2 rows)
>
>
> But this confuses me:
>
> => select x, sum(y) as foo from test1 group by x having foo>3 order
> by x;
> ERROR: column "foo" does not exist
> LINE 1: ...ect x, sum(y) as foo from test1 group by x having foo>3
> orde...
>
> Why isn't it possible to refer to a column alias in HAVING?
>
>
> --
> - Rikard
>
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