Oracle Database JOINS LEFT OUTER JOIN
Example
A LEFT OUTER JOIN performs a join between two tables that requires an explicit join clause but does not exclude unmatched rows from the first table.
Example:
SELECT
ENAME,
DNAME,
EMP.DEPTNO,
DEPT.DEPTNO
FROM
SCOTT.EMP LEFT OUTER JOIN SCOTT.DEPT
ON EMP.DEPTNO = DEPT.DEPTNO;
Even though ANSI syntax is the recommended way, it is likely to encounter legacy syntax very often. Using (+) within a condition determines which side of the equation to be considered as outer.
SELECT
ENAME,
DNAME,
EMP.DEPTNO,
DEPT.DEPTNO
FROM
SCOTT.EMP,
SCOTT.DEPT
WHERE
EMP.DEPTNO = DEPT.DEPTNO(+);
Here's an example of Left Outer Join between two tables:
Sample Table: EMPLOYEE
+-----------+---------+
| NAME | DEPTNO |
+-----------+---------+
| A | 2 |
| B | 1 |
| C | 3 |
| D | 2 |
| E | 1 |
| F | 1 |
| G | 4 |
| H | 4 |
+-----------+---------+
Sample Table: DEPT
+---------+--------------+
| DEPTNO | DEPTNAME |
+---------+--------------+
| 1 | ACCOUNTING |
| 2 | FINANCE |
| 5 | MARKETING |
| 6 | HR |
+---------+--------------+
Now, If you execute the query:
SELECT
*
FROM
EMPLOYEE LEFT OUTER JOIN DEPT
ON EMPLOYEE.DEPTNO = DEPT.DEPTNO;
Output:
+-----------+---------+---------+--------------+
| NAME | DEPTNO | DEPTNO | DEPTNAME |
+-----------+---------+---------+--------------+
| F | 1 | 1 | ACCOUNTING |
| E | 1 | 1 | ACCOUNTING |
| B | 1 | 1 | ACCOUNTING |
| D | 2 | 2 | FINANCE |
| A | 2 | 2 | FINANCE |
| C | 3 | | |
| H | 4 | | |
| G | 4 | | |
+-----------+---------+---------+--------------+
