SQL> CREATE TABLE a (a_id INT)
  2  /
 
Table created.
 
SQL> CREATE TABLE b (b_id INT, a_id INT)
  2  /
 
Table created.
 
SQL> CREATE TABLE c (c_id INT, b_id INT)
  2  /
 
Table created.
 
SQL> INSERT INTO a VALUES (1);
SQL> INSERT INTO a VALUES (2);
SQL> INSERT INTO a VALUES (3);
SQL> INSERT INTO b VALUES (165, 1);
SQL> INSERT INTO b VALUES (166, 2);
SQL> INSERT INTO c VALUES (7780, 165);
 
SQL> SET NULL [NULL]
SQL> SELECT   a.a_id
  2  ,        b.b_id
  3  ,        c.c_id
  4  FROM     a
  5  ,        b
  6  ,        c
  7  WHERE    a.a_id = b.a_id (+)
  8  AND      b.b_id = c.b_id (+)
  9  ORDER BY a.a_id
 10  /
 
      A_ID       B_ID       C_ID
---------- ---------- ----------
         1        165       7780
         2        166 [NULL]
         3 [NULL]     [NULL]
 
SQL> SELECT   a.a_id
  2  ,        b.b_id
  3  ,        c.c_id
  4  FROM     a LEFT OUTER JOIN b ON a.a_id = b.a_id
  5             LEFT OUTER JOIN c ON b.b_id = c.b_id
  6  ORDER BY a.a_id
  7  /
 
      A_ID       B_ID       C_ID
---------- ---------- ----------
         1        165       7780
         2        166 [NULL]
         3 [NULL]     [NULL]
 
SQL>