From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Amit Langote <amitlangote09@gmail.com>,
        Jacob Champion <jchampion@timescale.com>,
        Zhihong Yu <zyu@yugabyte.com>, David Rowley <dgrowleyml@gmail.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: generic plans and "initial" pruning
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Fri, 29 Jul 2022 11:56:02 -0400"
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Date: Fri, 29 Jul 2022 12:47:05 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> ... it's
> always struck me as a little unfortunate that we basically test
> whether a var is equal by testing whether the varno and varlevelsup
> are equal. That only works if you assume that you can never end up
> comparing two vars from thoroughly unrelated parts of the tree, such
> that the subquery one level up from one might be different from the
> subquery one level up from the other.

Yeah, that's always bothered me a little as well.  I've yet to see a
case where it causes a problem in practice.  But I think that if, say,
we were to try to do any sort of cross-query-level optimization, then
the ambiguity could rise up to bite us.  That might be a situation
where a flat rangetable would be worth the trouble.

> I'm just uncertain whether what Amit has implemented is the
> least-annoying way to go about it... any thoughts on that,
> specifically as it pertains to this patch?

I haven't looked at this patch at all.  I'll try to make some
time for it, but probably not today.

			regards, tom lane