Re: Understanding Aliases

> People frequently think that because ORDER BY can refer to the
> output-column aliases, other clauses should be able to do it too,
> but this is not so.

Thank you very much for clearing that one up.

Now I have a follow-up question. Let's assume that I want not only to
evaluate a subquery for the WHERE-statement, but also want to fetch the
result of this subquery. I think that this would be the correct way to do
so:

SELECT
            t2.id,
        (SELECT COUNT(id) FROM t4 WHERE t2_id = t2.id AND value=10)
AS t4_num
FROM
        t2
WHERE
        t2.active
            AND (
(SELECT COUNT(id) FROM t4 WHERE t2_id = t2.id AND value=10) <= 3
        )

Will the subquery be evaluated twice, or is postgres smart enough to somehow
cache the result from the first call of the subquery?

Kind Regards

Stanislav Raskin