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From: Richard Guo <[email protected]>
To: Tender Wang <[email protected]>
Cc: SATYANARAYANA NARLAPURAM <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Bug: var_is_nonnullable() gives wrong results for old/new in RETURNING
Date: Fri, 10 Apr 2026 14:48:34 +0900
Message-ID: <CAMbWs48swa+F+HmsxnVqYrSvDFgp9v7ShSjac5FsG4oFFKvs2w@mail.gmail.com> (raw)
In-Reply-To: <CAHewXN=9mf6NCeHE=7jUVhM_Ur=oW8R7hgfQwcvyWCSLC8VERw@mail.gmail.com>
References: <CAHg+QDfaAipL6YzOq2H=gAhKBbcUTYmfbAv+W1zueOfRKH43FQ@mail.gmail.com>
	<CAHewXN=9mf6NCeHE=7jUVhM_Ur=oW8R7hgfQwcvyWCSLC8VERw@mail.gmail.com>

On Fri, Apr 10, 2026 at 10:30 AM Tender Wang <[email protected]> wrote:
> SATYANARAYANA NARLAPURAM <[email protected]> 于2026年4月10日周五 02:43写道：
> > It appears the optimizer incorrectly simplifies old.<col> IS NULL to FALSE in RETURNING clauses when the underlying column has a NOT NULL constraint.
> >
> > The issue is that var_is_nonnullable() in clauses.c doesn't check Var.varreturningtype. 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 the old tuple doesn't exist on INSERT, and the new tuple doesn't exist on DELETE

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

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