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From: David Rowley <[email protected]>
To: [email protected]
To: [email protected]
To: Tom Lane <[email protected]>
Subject: Re: BUG #19412: Wrong query result with not null constraint
Date: Wed, 18 Feb 2026 11:53:50 +1300
Message-ID: <CAApHDvpXarz-D6tP-7y4ZrtnhXtdbRY0kQxRDQTVc3Z9DckYVw@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

On Wed, 18 Feb 2026 at 00:31, PG Bug reporting form
<[email protected]> 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 = a.x_id
> left join y on y.id = 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.

Tom, do you have any thoughts on the empty varnullingrels here?

David

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