PG17 compatibility: Fix Test Failure in local_dist_join_mixed

[m3hm3t]

PostgreSQL 16 adds an extra condition (id IS NOT NULL) to the subquery. This condition is likely used to ensure that no null values are processed in the subquery. Instead of using the condition id IS NOT NULL, PostgreSQL 17 generates the subplan with a trivial condition (WHERE true), indicating that it does not need to explicitly check for non-null values.

PostgreSQL 17 likely includes optimizations to handle null checks more efficiently. The WHERE (id IS NOT NULL) condition that was present in PostgreSQL 16 may now be considered redundant by the planner, as it is implicitly handled by the query execution engine.

postgres/postgres@b262ad44

 SELECT
        foo1.id
    FROM
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo9,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo8,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo7,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo6,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo5,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo4,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo3,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo2,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo10,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo1
 WHERE
  foo1.id =  foo9.id AND
  foo1.id =  foo8.id AND
  foo1.id =  foo7.id AND
  foo1.id =  foo6.id AND
  foo1.id =  foo5.id AND
  foo1.id =  foo4.id AND
  foo1.id =  foo3.id AND
  foo1.id =  foo2.id AND
  foo1.id =  foo10.id AND
  foo1.id =  foo1.id
ORDER BY 1;
...
-DEBUG:  generating subplan XXX_10 for subquery SELECT id FROM local_dist_join_mixed.local WHERE (id IS NOT NULL)
+DEBUG:  generating subplan XXX_10 for subquery SELECT id FROM local_dist_join_mixed.local WHERE true
...

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##             release-13.0    #7731   +/-   ##
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[naisila]

Here we can simply remove the redundant filter because it wasn't the original intention of this test.

 SELECT
        foo1.id
    FROM
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo9,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo8,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo7,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo6,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo5,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo4,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo3,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo2,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo10,
 (SELECT local.id, local.title FROM local, distributed WHERE local.id = distributed.id ) as foo1
 WHERE
  foo1.id =  foo9.id AND
  foo1.id =  foo8.id AND
  foo1.id =  foo7.id AND
  foo1.id =  foo6.id AND
  foo1.id =  foo5.id AND
  foo1.id =  foo4.id AND
  foo1.id =  foo3.id AND
  foo1.id =  foo2.id AND
  foo1.id =  foo10.id AND
-  foo1.id =  foo1.id
ORDER BY 1;

[naisila]

Since the filter was originally redundant without any special purpose, we can simply remove the redundant filter, no need for a normalize rule here.
#7731 (comment)

[naisila]

LGTM, thanks.

Reminder to rebase to release-13.0, and only include the changes related to local_dist_join_mixed.sql and local_dist_join_mixed.out