Re: PostgreSQL 10 changes in exclusion constraints - did something change? CASE WHEN behavior oddity

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2017-05-28 14:03:26 -0400, Tom Lane wrote:
>> I think it would be possible to teach eval_const_expressions that
>> it must not discard CASE/COALESCE subexpressions that contain SRFs,
>> which would preserve the rule that expression simplification doesn't
>> change the query semantics.

> That sounds like a good idea. Do you want to write up a patch, or
> should I? I can, but I'd want to finish the walsender panic and other
> signal handling stuff first (mostly waiting for review for now).

I think you've got enough on your plate. I can take care of whatever
we decide to do here. What I was looking for was opinions on which
way to address it.

>> Another possibility is to say that we've broken this situation
>> irretrievably and we should start throwing errors for SRFs in
>> places where they'd be conditionally evaluated. That's not real
>> nice perhaps, but it's better than the way things are right now.

> I'd be ok with that too, but I don't really see a strong need so far.

The argument for this way is basically that it's better to break
apps visibly than silently. The behavior for SRF-inside-CASE is
not going to be the same as before even if we implement the fix
I suggest above, and it's arguable that this new behavior is not
at all intuitive.

I'm not really sure which way to jump, which is why I was hoping
for some discussion here.

regards, tom lane