* Full outer join is basically a union all between an outer join and a anti join.
I.e. a union all of
  (test1 left outer join test2) and
  (all the rows in test2 not in test1) <- the anti join

* Hint seems only be able to reach the outer join part of the full outer join.
  Anti join part can not be hinted.
* However, full outer join can be decomposed into a union all of of the above mentioned
  2 selects. 2 hints can then be applied to them separatedly. Since the execution plan are
  identical, performance should be alike. Though the union all query would take a little 
  longer to parse, maybe negligible.
* This is also how full outer join was handled before ORACLE started supporting ANSI full 
  outer join syntax - with union all of outer join and anti join.
* Note that ORACLE will not obey the *_aj hints unless the columns involved are defined as
  NOT NULL.


SQL> select * from test1 full outer join test2 on test1.c1=test2.c1;


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=7 Card=24 Bytes=1080
          )

   1    0   VIEW (Cost=7 Card=24 Bytes=1080)
   2    1     UNION-ALL
   3    2       HASH JOIN (OUTER) (Cost=5 Card=23 Bytes=230)
   4    3         TABLE ACCESS (FULL) OF 'TEST1' (Cost=2 Card=23 Bytes
          =138)

   5    3         TABLE ACCESS (FULL) OF 'TEST2' (Cost=2 Card=9 Bytes=
          36)

   6    2       NESTED LOOPS (ANTI) (Cost=2 Card=1 Bytes=5)
   7    6         TABLE ACCESS (FULL) OF 'TEST2' (Cost=2 Card=9 Bytes=
          36)

   8    6         INDEX (RANGE SCAN) OF 'TEST_C1_IDX' (NON-UNIQUE)



SQL> select --+ use_merge(test2) 
  2  * from test1 full outer join test2 on test1.c1=test2.c1;


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=9 Card=24 Bytes=1080
          )

   1    0   VIEW (Cost=9 Card=24 Bytes=1080)
   2    1     UNION-ALL
   3    2       MERGE JOIN (OUTER) (Cost=7 Card=23 Bytes=230)
   4    3         SORT (JOIN) (Cost=4 Card=23 Bytes=138)
   5    4           TABLE ACCESS (FULL) OF 'TEST1' (Cost=2 Card=23 Byt
          es=138)

   6    3         SORT (JOIN) (Cost=4 Card=9 Bytes=36)
   7    6           TABLE ACCESS (FULL) OF 'TEST2' (Cost=2 Card=9 Byte
          s=36)

   8    2       NESTED LOOPS (ANTI) (Cost=2 Card=1 Bytes=5)
   9    8         TABLE ACCESS (FULL) OF 'TEST2' (Cost=2 Card=9 Bytes=
          36)

  10    8         INDEX (RANGE SCAN) OF 'TEST_C1_IDX' (NON-UNIQUE)



SQL> select * from test1 left outer join test2 on test1.c1=test2.c1
  2  union all
  3  select null,null,null,c1,c2 from test2 where test2.c1 not in (select /*+ merge_aj */ c1 from te
st1);


Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=12 Card=24 Bytes=235
          )

   1    0   UNION-ALL
   2    1     HASH JOIN (OUTER) (Cost=5 Card=23 Bytes=230)
   3    2       TABLE ACCESS (FULL) OF 'TEST1' (Cost=2 Card=23 Bytes=1
          38)

   4    2       TABLE ACCESS (FULL) OF 'TEST2' (Cost=2 Card=9 Bytes=36
          )

   5    1     MERGE JOIN (ANTI) (Cost=7 Card=1 Bytes=5)
   6    5       SORT (JOIN) (Cost=4 Card=9 Bytes=36)
   7    6         TABLE ACCESS (FULL) OF 'TEST2' (Cost=2 Card=9 Bytes=
          36)

   8    5       SORT (UNIQUE) (Cost=4 Card=23 Bytes=23)
   9    8         TABLE ACCESS (FULL) OF 'TEST1' (Cost=2 Card=23 Bytes
          =23)


SQL>