[HACKERS] Postgres_fdw join pushdown - INNER - FULL OUTER join combination generating wrong result

[Rajkumar Raghuwanshi]

Hi,

I am testing postgres_fdw join pushdown feature for PostgreSQL 9.6 DB, and
I observed below issue.

*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)

Thanks & Regards,
Rajkumar Raghuwanshi
QMG, EnterpriseDB Corporation

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