Re: Postgres_fdw join pushdown - INNER - FULL OUTER join combination generating wrong result

Observation:_ Inner join and full outer join combination on a table

generating wrong result.

SELECT * FROM lt;
  c1
----
   1
   2
(2 rows)

SELECT * FROM ft;
  c1
----
   1
   2
(2 rows)

\d+ ft
                              Foreign table "public.ft"
  Column |  Type   | Modifiers | FDW Options | Storage | Stats target |
Description
--------+---------+-----------+-------------+---------+--------------+-------------
  c1     | integer |           |             | plain   |              |
Server: link_server
FDW Options: (table_name 'lt')

--inner join and full outer join on local tables
SELECT t1.c1,t2.c1,t3.c1 FROM lt t1 INNER JOIN lt t2 ON (t1.c1 = t2.c1)
FULL JOIN lt t3 ON (t2.c1 = t3.c1);
  c1 | c1 | c1
----+----+----
   1 |  1 |  1
   2 |  2 |  2
(2 rows)

--inner join and full outer join on corresponding foreign tables
SELECT t1.c1,t2.c1,t3.c1 FROM ft t1 INNER JOIN ft t2 ON (t1.c1 = t2.c1)
FULL JOIN ft t3 ON (t2.c1 = t3.c1);
  c1 | c1 | c1
----+----+----
   1 |  1 |  1
   1 |  2 |
   2 |  1 |
   2 |  2 |  2
(4 rows)

I think the reason for that is in foreign_join_ok.  This in that function:

wrongly pulls up remote_conds from joining relations in the FULL JOIN case.  I think we should not pull up such conditions in the FULL JOIN case.