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
...

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.60%. Comparing base (b29c332) to head (0a8e7ab).

Additional details and impacted files

@@                   Coverage Diff                    @@
##           naisila/pg17_support    #7731      +/-   ##
========================================================
- Coverage                 89.61%   89.60%   -0.01%     
========================================================
  Files                       274      274              
  Lines                     59689    59689              
  Branches                   7446     7446              
========================================================
- Hits                      53490    53486       -4     
- Misses                     4069     4072       +3     
- Partials                   2130     2131       +1     

[naisila]

I am reluctant to merge a whole new test output for just a single line change. Let's think a bit more how we can fix this.