Rvsd. / Re: Named column in a Function fails at ORDER BY (PgSQL 7.1)

Hello Tom,
thanks for your detailed remarks.

At 03.04.2002 23:46, you wrote:
>...expressions over the input columns. Essentially it's a way to write
>
> SELECT content,
> datetime AS max_date,
> date_part('hour', datetime) AS order_val
> FROM cftext
> ORDER BY order_val
>
>(which would be a spec-legal construct) and then tell the system you
>didn't really want to see the order_val column in your output.

Actually I had not understood the input/output column rules with ORDER BY,
so my question was not meant as proposal to change the rules - in the first
place.

But at this occasion, now rethinking the concept of SQL92 vs. SQL99 (as you
describe them) I see some advantage of "expressions over output columns".
Once again, I just rewrote my query (simplified):

SELECT A, (SELECT x FROM y) AS B
FROM z
ORDER BY function ( A, B )

that did not work, into:

SELECT A, function ( A, (SELECT x FROM y) ) AS B
FROM z
ORDER BY B

That works fine, thanks so far.
But, if I wanted the subselect as an output column (as well as a function
parameter), I would have to write:

SELECT A, (SELECT x FROM y) AS B, function (A, B) AS C
FROM z
ORDER BY C

This once again does not work, because not only ORDER BY but also a
function() in the column list seems to fail with the output column name B.
The only workaround I see is to use the subselect twice - not very elegant.
(But I'm still willing to learn...)

>SQL99 seems to have (incompatibly) redefined ORDER BY to allow
>expressions over the output column names, but I don't have a lot of
>appetite for breaking existing applications in order to conform to the
>SQL99 definition.

Would it really break existing applications it this syntax would be possible?
Regards
// Bernd vdB