Re: subselects in the target list

Neil Conway <neilc(at)samurai(dot)com> writes:
> neilc=# select a, (select * from abc) from abc;
> ERROR: subquery must return only one column

> Is there a reason we can't treat a subselect in the target list as
> returning a composite type?

Given the 8.0 infrastructure for unnamed record types it might be
possible to do that; it was surely never possible before. Whether it's
a good idea is another question. The syntax you are showing is designed
to return a scalar. It will (and should) barf on multiple rows as well
as multiple columns.

> For that matter, is this behavior also intentional?

> neilc=# select a, foo_abc2() FROM abc;
> ERROR: set-valued function called in context that cannot accept a set
> CONTEXT: PL/pgSQL function "foo_abc2" line 1 at return next

It's an implementation restriction in plpgsql: we didn't make it support
the old-style SRF API. I'm unconvinced that it's worth fixing
considering that this whole behavior (SRFs in the targetlist) is
deprecated.

regards, tom lane