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From: Richard Guo <guofenglinux@gmail.com>
Date: Wed, 18 Feb 2026 10:51:40 +0900
Message-ID: <CAMbWs49kVgb_wS4VFuQpfZ+Re4tWVn7vmheR6HqKppnNuEaH-g@mail.gmail.com>
Subject: Re: BUG #19412: Wrong query result with not null constraint
To: David Rowley <dgrowleyml@gmail.com>
Cc: s.shinderuk@postgrespro.ru, pgsql-bugs@lists.postgresql.org, 
	Tom Lane <tgl@sss.pgh.pa.us>
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On Wed, Feb 18, 2026 at 7:54=E2=80=AFAM David Rowley <dgrowleyml@gmail.com>=
 wrote:
> On Wed, 18 Feb 2026 at 00:31, PG Bug reporting form
> <noreply@postgresql.org> wrote:
> > create table a (id int, x_id int, y_id int);
> > insert into a values (1, 1, 1), (1, 2, 2), (1, 3, 3);
> > create table x (id int, nm text, constraint pk_x_id primary key (id));
> > insert into x values (1, 'x1'), (2, 'x2'), (3, 'x3');
> > create table y (id int, nm text, constraint pk_y_id primary key (id));
> > insert into y values (1, 'y1'), (3, 'y3'), (4, 'y4');
> >
> > select a.id, z.id
> > from a
> > join x on x.id =3D a.x_id
> > left join y on y.id =3D a.y_id
> > join lateral(select x.id
> >              union all
> >              select y.id) z on z.id is not null;

> Thanks for the reproducer.
>
> I'd say that y.id Var in the lateral join should be getting marked as
> nullable by the left join, but it's not being marked as nullable by
> anything.

Exactly.  I think this is because when adjust_appendrel_attrs_mutator
propagates the nullingrel bits from the parent rel's Var into the
translated Var, it loses the translated Var's original bits.  Instead
of overwriting the translated Var's nullingrels, I think we should
merge them.

--- a/src/backend/optimizer/util/appendinfo.c
+++ b/src/backend/optimizer/util/appendinfo.c
@@ -291,8 +291,11 @@ adjust_appendrel_attrs_mutator(Node *node,
                 var->varattno, get_rel_name(appinfo->parent_reloid));
        if (IsA(newnode, Var))
        {
-           ((Var *) newnode)->varreturningtype =3D var->varreturningtype;
-           ((Var *) newnode)->varnullingrels =3D var->varnullingrels;
+           Var    *newvar =3D (Var *) newnode;
+
+           newvar->varreturningtype =3D var->varreturningtype;
+           newvar->varnullingrels =3D bms_add_members(newvar->varnullingre=
ls,
+                                                    var->varnullingrels);
        }

- Richard