How To Write a Left Outer Join with the WHERE Clause? - Oracle DBA FAQ - Understanding SQL SELECT Query Statements

If you don't want to use the LEFT OUTER JOIN ... ON clause to write a left outer join, you can use a special criteria in the WHERE clause as "left_table.column = right_table.column(+)". The select statement below is an example of a left outer join written with the WHERE clause:

SQL> set NULL 'NULL'
SQL> SELECT d.department_name, e.first_name, e.last_name 
  2  FROM departments d, employees e 
  3  WHERE d.manager_id = e.employee_id(+);

DEPARTMENT_NAME           FIRST_NAME           LAST_NAME
-------------------- -------------------- --------------
Administration            Jennifer             Whalen
Marketing                 Michael              Hartstein
Purchasing                Den                  Raphaely
Human Resources           Susan                Mavris
Shipping                  Adam                 Fripp
IT                        Alexander            Hunold
......
Treasury                  NULL                 NULL
Corporate Tax             NULL                 NULL
Control And Credit        NULL                 NULL
Shareholder Services      NULL                 NULL
Benefits                  NULL                 NULL
Manufacturing             NULL                 NULL
......

Note that a left outer join may return extra rows from the first (left) table that do not satisfy the join condition. In those extra rows, columns from the second (right) table will be given null values.

The extra rows returned from the left outer join in this example represents departments that have no manager IDs.