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From: Richard Guo <guofenglinux@gmail.com>
Date: Fri, 10 Apr 2026 14:48:34 +0900
Message-ID: 
 <CAMbWs48swa+F+HmsxnVqYrSvDFgp9v7ShSjac5FsG4oFFKvs2w@mail.gmail.com>
Subject: Re: Bug: var_is_nonnullable() gives wrong results for old/new in
 RETURNING
To: Tender Wang <tndrwang@gmail.com>
Cc: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Fri, Apr 10, 2026 at 10:30=E2=80=AFAM Tender Wang <tndrwang@gmail.com> w=
rote:
> SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com> =E4=BA=8E2026=E5=B9=
=B44=E6=9C=8810=E6=97=A5=E5=91=A8=E4=BA=94 02:43=E5=86=99=E9=81=93=EF=BC=9A
> > It appears the optimizer incorrectly simplifies old.<col> IS NULL to FA=
LSE in RETURNING clauses when the underlying column has a NOT NULL constrai=
nt.
> >
> > The issue is that var_is_nonnullable() in clauses.c doesn't check Var.v=
arreturningtype. It sees a NOT NULL column and concludes the Var can never =
be NULL.
> > But this assumption is wrong for old.* and new.* references. Because th=
e old tuple doesn't exist on INSERT, and the new tuple doesn't exist on DEL=
ETE

Nice catch.

> Yes,  the current var_is_nonnullable() ignores this case.  The
> attached patch seems ok to me.

The patch also LGTM.  I also checked if has_notnull_forced_var() has
the same issue, but it doesn't: Vars with non-default returning type
only appear in the RETURNING clause, so they never show up in WHERE/ON
clauses.

- Richard