How To Write a Query with a Full Outer Join?

If you want to query from two tables with a full outer join, you can use the FULL OUTER JOIN ...
ON clause in the FROM clause. The following query returns output with a full outer join from two
tables: departments and employees. The join condition is that the manager ID in the departments
table equals to the employee ID in the employees table:
SQL> set NULL 'NULL'
SQL> SELECT d.department_name, e.first_name, e.last_name
FROM departments d FULL OUTER JOIN employees e
ON 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
Construction NULL NULL
......
NULL Clara Vishney
NULL Jason Mallin
NULL Hazel Philtanker
NULL Nanette Cambrault
NULL Alana Walsh
NULL Karen Partners
NULL Bruce Ernst
......
Note that a right outer join may return two sets of extra rows: one set from the first (left) table that
do not satisfy the join condition, and the other set from the second (right) table that do not satisfy
the join condition.