Re: Alias in the HAVING clause

Oops, that second query should be
SELECT COUNT(*), id % 3 AS f1 FROM table GROUP BY f1 HAVING id % 3 <> 0;

On Tue, May 13, 2008 at 3:43 PM, Nathan Thatcher <n8thatcher(at)gmail(dot)com> wrote:
> I am in the middle of switching a bunch of queries over from MySQL to
> PostgreSQL and have hit a little snag. The following query works fine
> in MySQL but raises an error in postgres:
>
> SELECT COUNT(*), id % 3 AS f1 FROM table GROUP BY f1 HAVING f1 <> 0;
>
> It seems that Postgres does not recognize the alias in the HAVING
> clause. Rewriting it like this works in postgres:
>
> SELECT COUNT(*), id % 3 AS f1 FROM table GROUP BY f1 HAVING event_id % 3 <> 0;
>
> I am wondering if I am missing something because this looks like my
> expression (id % 3) is getting evaluated twice when it really only
> should be done once. Now, this query is obviously watered down from
> what I am really doing and the expression is fairly lengthy and
> complex so I would prefer to not have to evaluate it more times than
> necessary.
>
> Is this the correct way to do this, or is there a better way / a way
> to get PostgreSQL to recognize an alias in the HAVING clause?
>
> Thanks,
> Nate
>