Prevent Parallel Hash Join for JOIN_UNIQUE_INNER.
Prevent Parallel Hash Join for JOIN_UNIQUE_INNER.

WHERE EXISTS (...) queries cannot be executed by Parallel Hash Join
with jointype JOIN_UNIQUE_INNER, because there is no way to make a
partial plan totally unique.  The consequence of allowing such plans
was duplicate results from some EXISTS queries.

Back-patch to 11.  Bug #15857.

Author: Thomas Munro
Reviewed-by: Tom Lane
Reported-by: Vladimir Kriukov
Discussion: https://postgr.es/m/15857-d1ba2a64bce0795e%40postgresql.org

lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,adam8157/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb