From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
cc: pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Avoid mislabeling of lateral references when pulling up a
 subque
In-reply-to: 
 <CAMbWs48E8xR4T3G2ynFGGzh3nQ1zNwuxq_Fn92-gWGDr7As_cw@mail.gmail.com>
References: <E1tGn4j-0003zi-MP@gemulon.postgresql.org>
 <CAMbWs4-4vf7XvYHjQBqsA67zaLdmyKPaznFw78Kcp9mxdqMKEw@mail.gmail.com>
 <397371.1732844670@sss.pgh.pa.us>
 <CAMbWs4-iZiWWb_KYJJEZ0=zQSD0WNwz_hvNTT3uABCVQNKP7Mg@mail.gmail.com>
 <530989.1732907849@sss.pgh.pa.us> <590235.1732915884@sss.pgh.pa.us>
 <CAMbWs48E8xR4T3G2ynFGGzh3nQ1zNwuxq_Fn92-gWGDr7As_cw@mail.gmail.com>
Comments: In-reply-to Richard Guo <guofenglinux@gmail.com>
	message dated "Sat, 30 Nov 2024 12:09:18 +0900"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <824290.1732937102.1@sss.pgh.pa.us>
Date: Fri, 29 Nov 2024 22:25:02 -0500
Message-ID: <824291.1732937102@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/824291.1732937102%40sss.pgh.pa.us>
Precedence: bulk

Richard Guo <guofenglinux@gmail.com> writes:
> This patch can also simplify my other patch, which is to avoid
> unnecessary wrapping for plain Vars/PHVs.  We can check the new
> nullingrel_info to see if the nullingrels of the subquery RTE are a
> subset of the nullingrels of the lateral referenced rel, to determine
> if the referenced rel is under the same lowest nulling outer join.
> And this eliminates the need to introduce lowest_nullable_side.

Right, because that's more or less the same problem.  Or indeed
it's exactly the same problem, we're just making fast paths for
the easiest cases.

Another thought: the reason I made get_nullingrels return a new
struct rather than tying it directly to filling some fields in
pullup_replace_vars_context was that I think we might want to
reconsider where to call it from.  Perhaps it'd be useful to
have the info during is_simple_subquery, for example.

			regards, tom lane