Outer join

From Oracle FAQ

An outer join is similar to the equi join, but Oracle will also return non matched rows from the table with the outer join operator (+). Missing values are filled with NULL values.

Examples

Using Oracle join syntax:

SELECT e.ename, d.dname
  FROM emp e, dept d
 WHERE e.deptno = d.deptno(+);

SELECT e.ename, d.dname
  FROM emp e, dept d
 WHERE e.deptno(+) = d.deptno; 

Note: The (+) sign indicates that in case the column contains a null it should also be included.

Using ANSI join syntax:

SELECT e.ename, d.dname
  FROM emp e LEFT OUTER JOIN dept d
    ON (e.deptno = d.deptno);

SELECT e.ename, d.dname
  FROM emp e RIGHT OUTER JOIN dept d
    ON (e.deptno = d.deptno);

Full outer joins can only be performed using the ANSI syntax:

SELECT e.ename, d.deptno
  FROM emp e FULL OUTER JOIN dept d
    ON (e.deptno = d.deptno);

Also see

Articles:

• Common errors seen when using OUTER-JOIN

Other join methods:

• Cartesian join
• Equi join
• Inner join
• Natural join
• Nonequi join
• Self join

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