-- Note that row 7 has NULL in both columns
SQL> select * from tyu;

        C1         C2
---------- ----------
         1         11
         2         12
         3         13
         1          3
         7          8
         3          3
                        <-- NULL and NULL
                   77
        88

9 rows selected.


-- Note that col1 of row 5 is NULL
SQL> select * from tyu2;

      COL1 COL2
---------- ----------
         1 1_row
        12 2_row
         3 3_row
       100 4_row
           null_row

-- Give me all the stuff from tyu
-- Give me all the stuff from tyu2 only when both columns in tyu matches
--         col1 in tyu2
SQL>  select * from tyu, tyu2 t2
  2   where c1=t2.col1(+) and c2=t2.col1(+);

        C1         C2       COL1 COL2
---------- ---------- ---------- ----------
         1          3
         1         11
         2         12
         3          3          3 3_row
         3         13
         7          8
        88
                   77


9 rows selected.

-- Give me all the stuff from tyu
-- Give me all the stuff from tyu2 as long as one column in tyu
--             matches col1 in tyu2
SQL> select * from tyu, tyu2 t2, tyu2 t3
  2  where c1=t2.col1(+) and c2=t3.col1(+);

        C1         C2       COL1 COL2             COL1 COL2
---------- ---------- ---------- ---------- ---------- ----------
         1          3          1 1_row               3 3_row
         1         11          1 1_row
         2         12                               12 2_row
         3          3          3 3_row               3 3_row
         3         13          3 3_row
         7          8
        88
                   77


9 rows selected.