From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: zuming.jiang@inf.ethz.ch, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17976: Inconsistent results of SELECT using CASE WHEN clause
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Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Thu, 15 Jun 2023 11:22:55 +1200"
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Date: Wed, 14 Jun 2023 19:55:27 -0400
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David Rowley <dgrowleyml@gmail.com> writes:
> The first bad commit seems to be b448f1c8

Yeah, I think the proximate cause is the removal of the delay_upper_joins
restrictions in analyzejoins.c.  That allows us to remove the join to
ref_0, which prior versions didn't do; but then that exposes the need to
clean up dead references in EquivalenceClasses.  I'm wondering a bit
now if there are variants of this that'd fail in pre-v16 branches.
It's not obvious to me offhand why delay_upper_joins would have prevented
all cases where a removable rel could be mentioned in an EquivalenceClass
member (presumably via the ph_rels set of a PHV).

			regards, tom lane