Re: [HACKERS] Implement targetlist SRFs using ROWS FROM() (was Changed SRF in targetlist handling)

Robert Haas <robertmhaas@gmail.com> writes:
> So, one of the big reasons I use CASE is to avoid evaluating
> expressions in cases where they might throw an ERROR.  Like, you know:
> CASE WHEN d != 0 THEN n / d ELSE NULL END
> I guess it's not the end of the world if that only works for
> non-set-returning functions, but it's something to think about.

Well, refusing CASE-containing-SRF at all isn't going to make your
life any better in that regard :-(

It's possibly worth noting that this is also true for aggregates and
window functions: wrapping those in a CASE doesn't stop them from being
evaluated, either.  People seem to be generally used to that, although
I think I've seen one or two complaints about it from folks who seemed
unclear on the concept of aggregates.

In the end I think this is mostly about backwards compatibility:
are we sufficiently worried about that that we'd rather throw an
error than have a silent change of behavior?  TBH I'm not sure.
We've certainly got two other silent changes of behavior in this
same patch.  The argument for treating this one differently,
I think, is that it's changing from a less surprising behavior
to a more surprising one whereas the other changes are the reverse,
or at worst neutral.
        regards, tom lane