Fix thinko in qual distribution.

deconstruct_distribute tweaks the outer join scope (ojscope)
it passes to distribute_qual_to_rels when considering an outer
join qual that's above potentially-commutable outer joins.
However, if the current join is *not* potentially commutable,
we shouldn't do that.  The argument that distribute_qual_to_rels
will not do something wrong with the bogus ojscope falls flat
if we don't pass it non-null postponed_oj_qual_list.  Moreover,
there's no need to play games in this case since we aren't going
to commute anything.

Per SQLSmith testing by Robins Tharakan.

Discussion: https://postgr.es/m/CAEP4nAw74k4b-=93gmfCNX3MOY3y4uPxqbk_MnCVEpdsqHJVsg@mail.gmail.com

1 files changed, 18 insertions, 0 deletions

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index c520839bf7..9762952efd 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -4451,6 +4451,24 @@ select * from
  doh! | 123 | 456 | hi de ho neighbor |   
 (2 rows)
 
+-- check handling of a variable-free qual for a non-commutable outer join
+explain (costs off)
+select nspname
+from (select 1 as x) ss1
+left join
+( select n.nspname, c.relname
+  from pg_class c left join pg_namespace n on n.oid = c.relnamespace
+  where c.relkind = 'r'
+) ss2 on false;
+           QUERY PLAN           
+--------------------------------
+ Nested Loop Left Join
+   Join Filter: false
+   ->  Result
+   ->  Result
+         One-Time Filter: false
+(5 rows)
+
 --
 -- test for appropriate join order in the presence of lateral references
 --