Re: Reduce "Var IS [NOT] NULL" quals during constant folding

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Before we commit to something along these lines, I think we need to
> understand whether Tom intends to press Peter for some bigger change
> around expand_virtual_generated_columns.
> If Tom doesn't respond right away, I suggest that we need to add an
> open item for http://postgr.es/m/602561.1744314879@sss.pgh.pa.us

I think that we do need to do something about that, but it may be
in the too-late-for-v18 category by now. Not sure. I definitely
don't love the idea of table_open'ing every table in every query
an extra time just to find out (about 99.44% of the time) that it
does not have any virtual generated columns.

I wonder if a better answer would be to make the rewriter responsible
for this. If you hold your head at the correct angle, a table with
virtual generated columns looks a good deal like a view, and we don't
ask the planner to handle those.

BTW, in my mind the current thread is certainly v19 material,
so I have not looked at Richard's patch yet.

regards, tom lane