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Subject: BUG #19579: Wrong results regression
To: pgsql-bugs@lists.postgresql.org
From: PG Bug reporting form <noreply@postgresql.org>
Cc: leis@in.tum.de
Reply-To: leis@in.tum.de, pgsql-bugs@lists.postgresql.org
Date: Sat, 25 Jul 2026 07:19:01 +0000
Message-ID: <19579-e6296b6c9fc0591c@postgresql.org>
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The following bug has been logged on the website:

Bug reference:      19579
Logged by:          Viktor Leis
Email address:      leis@in.tum.de
PostgreSQL version: 19beta2
Operating system:   Ubuntu 26.04 LTS
Description:       =20

Hi,

The following self-contained query returns rows on current master and on
19beta2, but should return nothing.  PostgreSQL 18 and earlier are
unaffected.

  select * from
    (select 0 as c0 from
       (select t1.c0 from
          (select null::int as c0 from ((select 1) union all (select 2)) t0)
t1
        full join (select 1 as c1 where false) t2 on true) t3
     where c0 <> 7) t4
    cross join (select * from (values (0::bigint)) v(x)
                where now() is not null) t5;

   c0 | x
  ----+---
    0 | 0
    0 | 0
  (2 rows)

t1.c0 is a plain NULL::integer, so "c0 <> 7" is NULL for every row and
nothing should survive it.  EXPLAIN (VERBOSE, COSTS OFF) shows that the
filter is simply gone:

   Result
     Output: 0, '0'::bigint
     ->  Append
           ->  Result
                 One-Time Filter: (now() IS NOT NULL)
           ->  Result
                 One-Time Filter: (now() IS NOT NULL)

Bisection points to commit f2bae51dfd5 ("Keep track of what RTIs a Result
node is scanning", 2025-09-23).

Best regards,
Viktor Leis