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Oracle Tutorials - Query with a Left Outer Join

By: FYIcenter.com

(Continued from previous topic...)

How To Write a Query with a Left Outer Join?

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.

(Continued on next topic...)

  1. What Is a SELECT Query Statement?
  2. How To Select All Columns of All Rows from a Table?
  3. How To Select Some Columns from a Table?
  4. How To Select Some Rows from a Table?
  5. How To Sort the Query Output?
  6. Can the Query Output Be Sorted by Multiple Columns?
  7. How To Sort Query Output in Descending Order?
  8. How To Use SELECT Statement to Count the Number of Rows?
  9. Can SELECT Statements Be Used on Views?
  10. How To Filter Out Duplications in Returning Rows?
  11. What Are Group Functions?
  12. How To Use Group Functions in the SELECT Clause?
  13. Can Group Functions Be Mixed with Non-group Selection Fields?
  14. How To Divide Query Output into Groups?
  15. How To Apply Filtering Criteria at Group Level?
  16. How To Count Duplicated Values in a Column?
  17. Can Multiple Columns Be Used in GROUP BY?
  18. Can Group Functions Be Used in the ORDER BY Clause?
  19. How To Join Two Tables in a Single Query?
  20. How To Write a Query with an Inner Join?
  21. How To Define and Use Table Alias Names?
  22. How To Write a Query with a Left Outer Join?
  23. How To Write a Query with a Right Outer Join?
  24. How To Write a Query with a Full Outer Join?
  25. How To Write an Inner Join with the WHERE Clause?
  26. How To Write a Left Outer Join with the WHERE Clause?
  27. How To Name Query Output Columns?
  28. What Is a Subquery?
  29. How To Use Subqueries with the IN Operator?
  30. How To Use Subqueries with the EXISTS Operator?
  31. How To Use Subqueries in the FROM Clause?
  32. How To Count Groups Returned with the GROUP BY Clause?
  33. How To Return Top 5 Rows?

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