Left Vs Right Outer Join Which is Better

The concept of JOINS in SQL is to get data from multiple Tables. In DB2, you can find two types of outer joins – LEFT outer and RIGHT outer JOINS.

There is no difference between a left outer join and right outer join other than where the starting driver table is coded

LEFT Outer JOIN


SELECT D.DEPTNO, D.DEPTNAME, D.MGRNO,
E.LASTNAME
FROM DEPT D LEFT JOIN
EMP E ON D.MGRNO = E.EMPNO

Right Outer JOIN


SELECT D.DEPTNO, D.DEPTNAME, D.MGRNO,
E.LASTNAME
FROM EMP E RIGHT JOIN
DEPT D ON D.MGRNO = E.EMPNO

When you give LEFT join, the driver table will be left side one. When you give RIGHT join, then the driver table will be right side one.

LEFT outer Join is Better Why

DB2 itself converts RIGHT outer JOIN into LEFT outer JOIN during SQL query processing
So to avoid confusion and save CPU time always code only LEFT OUTER join
This improves your SQL query performance

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