From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Regina Obe <lr@pcorp.us>,
        "'PostgreSQL-development'" <pgsql-hackers@postgresql.org>
Subject: Re: PostgreSQL 10 changes in exclusion constraints - did something
 change? CASE WHEN behavior oddity
In-reply-to: <20170603024503.yv6gxvkyx6mtc63m@alap3.anarazel.de>
References: <000001d2d5de$d8d66170$8a832450$@pcorp.us>
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 <21809.1495994606@sss.pgh.pa.us>
 <20170603024503.yv6gxvkyx6mtc63m@alap3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Fri, 02 Jun 2017 19:45:03 -0700"
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Date: Fri, 02 Jun 2017 22:53:00 -0400
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Andres Freund <andres@anarazel.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


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