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  Oracle SQL self joins

Self-joins can get ugly 

Visually, it sometimes helps to look at the table as two identical tables (A and B).  I am joining A to B, it just happens to be the same table.  Because the table is used twice in the query, you must alias the table, and of course, you cannot use a natural join.  In the example below, I want a list of employees and their managers.  In the EMP table, each employee is identified by an emp_key.  The employee's manager is in the manager column and it contains the manager's emp_key.

SQL> select
  2    b.emp_last_name EMPLOYEE,
  3    a.emp_last_name MANAGER
  4  from
  5    emp a right outer join emp b on (a.emp_key = b.manager); 
EMPLOYEE                       MANAGER
------------------------------ -------------------------
brannigan                      king
coleman                        king
baker                          king
johnson                        king
levender                       king
tokheim                        king
linus                          king
korn                           king
jackson                        king
king
10 rows selected
 
 
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