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How To Write a Query with a Left Outer Join
How To Write a Query with a Left Outer Join? - Oracle DBA FAQ - Understanding SQL SELECT Query Statements
✍: FYIcenter.com
If you want to query from two tables with a left outer join, you can use the LEFT OUTER JOIN ... ON clause in the FROM clause. The following query returns output with a left outer join from two tables: departments and employees. The join condition is that the manager ID in the departments table equals to the employee ID in the employees table:
SQL> set NULL 'NULL' SQL> SELECT d.department_name, e.first_name, e.last_name 2 FROM departments d LEFT OUTER JOIN employees e 3 ON d.manager_id = e.employee_id; DEPARTMENT_NAME FIRST_NAME LAST_NAME -------------------- -------------------- -------------- Administration Jennifer Whalen Marketing Michael Hartstein Purchasing Den Raphaely Human Resources Susan Mavris Shipping Adam Fripp IT Alexander Hunold ...... Treasury NULL NULL Corporate Tax NULL NULL Control And Credit NULL NULL Shareholder Services NULL NULL Benefits NULL NULL Manufacturing NULL NULL Construction NULL NULL ......
Note that a left outer join may return extra rows from the first (left) table that do not satisfy the join condition. In those extra rows, columns from the second (right) table will be given null values.
The extra rows returned from the left outer join in this example represents departments that have no manager IDs.
2007-04-19, 4786👍, 0💬
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