Ken Tanzer <ken.tanzer@gmail.com> writes:
> But thinking about it some more, the function runs one of 5 possible
> queries. 4 of them select NULL as comment (no cast), while the fifth (and
> the one that caused this error) selects 'a string'.
Ah. Fixing that so all the variants produce the same (explicit) type
should take care of this.
> I assume this will go away if I change my lazy query and cast my NULLs, but
> still wonder if this is something that should be expected to fail?
Ideally it wouldn't, but it's not clear what it'd cost to fix it.
If we just silently replanned when the query output types changed,
then this type of situation would work but would carry a large hidden
performance penalty. That's not too appetizing either.
regards, tom lane