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Oracle Tutorials - Query with a Left Outer Join
(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...)
- What Is a SELECT Query Statement?
- How To Select All Columns of All Rows from a Table?
- How To Select Some Columns from a Table?
- How To Select Some Rows from a Table?
- How To Sort the Query Output?
- Can the Query Output Be Sorted by Multiple Columns?
- How To Sort Query Output in Descending Order?
- How To Use SELECT Statement to Count the Number of Rows?
- Can SELECT Statements Be Used on Views?
- How To Filter Out Duplications in Returning Rows?
- What Are Group Functions?
- How To Use Group Functions in the SELECT Clause?
- Can Group Functions Be Mixed with Non-group Selection Fields?
- How To Divide Query Output into Groups?
- How To Apply Filtering Criteria at Group Level?
- How To Count Duplicated Values in a Column?
- Can Multiple Columns Be Used in GROUP BY?
- Can Group Functions Be Used in the ORDER BY Clause?
- How To Join Two Tables in a Single Query?
- How To Write a Query with an Inner Join?
- How To Define and Use Table Alias Names?
- How To Write a Query with a Left Outer Join?
- How To Write a Query with a Right Outer Join?
- How To Write a Query with a Full Outer Join?
- How To Write an Inner Join with the WHERE Clause?
- How To Write a Left Outer Join with the WHERE Clause?
- How To Name Query Output Columns?
- What Is a Subquery?
- How To Use Subqueries with the IN Operator?
- How To Use Subqueries with the EXISTS Operator?
- How To Use Subqueries in the FROM Clause?
- How To Count Groups Returned with the GROUP BY Clause?
- How To Return Top 5 Rows?