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SQL RIGHT Join

Tuesday, December 06, 2011

tags SQL

The SQL RIGHT JOIN keyword returns all rows from the RIGHT table, even if there are no matches in the LEFT table.

Departments Table

deptNameemployeeID
Sales1000
HR1002
Accounting1003
Operations1004


Employees Table

employeeIDemployeeName
1000John Smith
1001Fred White
1002Jane Scott
1003Samuel Williams

In this example, employeeID is a primary key in the table called "Employees". You'll notice that employeeID also exists in the "Departments" table, but as a foreign key. Using an SQL Join, we can combine these two tables into one when presenting the results of a query.


Design Example

In this example, using a RIGHT JOIN, we can build a query to display the departments and employees even though not every employee is assigned to a department, such as in the case of 'Fred White'.  The two tables are joined by the 'employeeID' field. We can use the RIGHT JOIN to bind this data together.


SQL Right Join

Syntax

SELECT tableName#.columnName#, tableName#.columnName#, etc...
FROM tableName1
RIGHT JOIN tableName2
ON tableName1.columnName# = tableName2.columnName#


Example

List the departments and their assigned employees.

SELECT Departments.deptName, Employees.employeeName
FROM Departments
RIGHT JOIN Employees
ON Departments.employeeID = Employees.employeeID


Results

deptNameemployeeName
SalesJohn Smith
 Fred White
HRJane Scott
AccountingSamuel Williams


You should immediately notice that 'Fred White' from the Employees table is listed. This is because there is there is no department assigned to 'Fred White' and we had specific a RIGHT JOIN in the query.   If there are rows in "Departments" that do not have matches in "Employees", the records from Employees will be returned in the result set.

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SQL Cookbook Head First SQL: Your Brain on SQL A Learners Guide