Re: Identity projection

Amit Kapila <amit(dot)kapila(at)huawei(dot)com> writes:
> On Friday, February 08, 2013 12:00 AM Tom Lane wrote:
> As per my understanding, currently in code wherever Result node can be
> avoided,
> it calls function is_projection_capable_plan(), so we can even enhance
> is_projection_capable_plan()
> so that it can also verify the expressions of tlists. But for this we need
> to change at all places
> from where is_projection_capable_plan() is called.

Hm. Really there's a whole dance that typically goes on, which is like

if (!is_projection_capable_plan(result_plan))
{
result_plan = (Plan *) make_result(root,
sub_tlist,
NULL,
result_plan);
}
else
{
/*
* Otherwise, just replace the subplan's flat tlist with
* the desired tlist.
*/
result_plan->targetlist = sub_tlist;
}

Perhaps we could encapsulate this whole sequence into a function called
say assign_targetlist_to_plan(), which would have the responsibility to
decide whether a Result node needs to be inserted.

regards, tom lane