Re: Bug: var_is_nonnullable() gives wrong results for old/new in RETURNING

On Fri, Apr 10, 2026 at 10:30 AM Tender Wang <tndrwang(at)gmail(dot)com> wrote:
> SATYANARAYANA NARLAPURAM <satyanarlapuram(at)gmail(dot)com> 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