Outer Join: The use of Outer Join is that it still joins those tuples that do not have matching values in common columns are also contained in the result table. Outer join places null values in columns where there is not a match among tables. A condition involving an outer join is that it cannot use the IN operator or cannot be related to another condition by the OR operator.

Example:

There is an example of left outer join (which only considers the non-matching tuples of table on the left side of the join expression).

SELECT CUSTOMER.CUTOID, CUSTONAME, ORDERID

 FROM CUSTOMER LEFT OUTER JOIN ORDER

WHERE CUSTOMER.CUSTOID =   ORDER.CUSTOID;

Output: The following result suppose a CUSTID in CUSTOMER table who have not issued any order so far.

CUSTOID                  CUSTONAME                        ORDERID

-------------------          ----------------------    ------------

10                           Pooja Enterprises                   1001

12                           Estern Enterprises                 1002

3                             Impressions                          1003

15                          South Enterprises                   NULL

The other types of outer join are the Right outer join or complete outer join.