On Fri, Aug 21, 2009 at 12:05:51PM -0400, Tom Lane wrote:
> Sam Mason <sam@samason.me.uk> writes:
> > ... PG should instead arrange that the expression
> > "t" is run exactly once and reuse the single result for all columns.
>
> We might be able to do that based on the row-returning-subselect
> infrastructure being discussed over here:
> http://archives.postgresql.org/message-id/4087.1250867036@sss.pgh.pa.us
Huh, fun. Not sure if I'm interpreting this correctly, but what would
the difference in semantics between:
SELECT (SELECT 1,2);
and
SELECT (SELECT (1,2));
PG seems to make the distinction somewhat blurry at the moment. For
example, upthread I did:
SELECT (id((SELECT (1,2)::foo))).*;
and got back two columns, and yet when I do what I think is equivalent:
SELECT x.*
FROM (SELECT (1,2)::foo) x;
I get back my tuple, and not the values inside my tuple.
Should I be posting this to -hackers?
--
Sam http://samason.me.uk/
