Re: [HACKERS] Why not sub-selects in targetlists?

Tom Lane wrote:
> 
> For some reason we currently support sub-SELECT expressions only
> in WHERE and HAVING clauses, not in the target list of a SELECT.
> Does anyone know why this is?
> 
> There are a number of places in the planner/optimizer that would need
> to be fixed to make it happen, but the changes are utterly trivial
> (calling certain transformation routines on the targetlist as well as
> for WHERE and HAVING ... probably about a dozen lines total ...).
> And a quick look at the executor doesn't show any reason why it would
> have a problem, either.  Is there something fundamental that I'm
> missing?  If not, why wasn't this done to begin with?

As usual, I just hadn't time to do more than it's done for
6.3.X -:) Subselects were not in my TODO list, I made base
implementation because of there were many requests for them.

BTW, please don't forget subselects in FROM.

Vadim