Excerpts from Peter Eisentraut's message of mié jul 21 15:18:58 -0400 2010:
> After some investigation I figured that I need to add two more checks
> into the ALTER TABLE code to prevent certain types of direct changes to
> typed tables (see attached patch).
>
> But it's not clear to me whether such checks should go into the "Prep"
> or the "Exec" phases. Prep seems more plausible to me, but some
> commands such as DropColumn don't have a Prep handler. A clarification
> would be helpful.
I think if there's no Prep phase, you should add it. I don't think it
makes sense to have this kind of check in Exec.