From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, Mark Dilger <hornschnorter(at)gmail(dot)com>, Regina Obe <lr(at)pcorp(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: PostgreSQL 10 changes in exclusion constraints - did something change? CASE WHEN behavior oddity |
Date: | 2017-06-11 18:18:41 |
Message-ID: | 28631.1497205121@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> Interesting stuff. Here's a small recommendation for a couple of those
> new messages.
Hm. I don't object to folding those two messages into one, but now that
I look at it, the text needs some more work anyway, perhaps. What we're
actually checking is not so much whether the IS DISTINCT FROM construct
returns a set as whether the underlying equality operator does. If we
want to be pedantic about it, we'd end up writing something like
"equality operator used by %s must not return a set"
But perhaps it's okay to fuzz the distinction and just write
"%s must not return a set"
You could justify that on the reasoning that if we were to allow this
then an underlying "=" that returned a set would presumably cause
IS DISTINCT FROM or NULLIF to also return a set.
I'm kind of thinking that the second wording is preferable, but there's
room to argue that the first is more precise. Opinions?
regards, tom lane
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