When working with multiple tables in a relational database system, it is often necessary to retrieve data from these tables using joins. One type of join that is commonly used is the SQL Outer Join. In this article, we will provide a comprehensive overview of the SQL Outer Join, including its types and examples.

Overview of the SQL Outer Join

The SQL Outer Join is used to match rows between tables and retrieve both matching and unmatched rows from one or both of the tables. There are three types of SQL Outer Joins:

• SQL Full Outer Join
• SQL Left Outer Join
• SQL Right Outer Join

SQL Full Outer Join

In a SQL Full Outer Join, all rows from both tables are included in the result set. If there are any unmatched rows, NULL values are shown for them. Let’s consider an example to understand this better.

SELECT * 
FROM Employee 
FULL OUTER JOIN Departments 
ON Employee.EmpID = Departments.EmpID;

In the above query, we perform a Full Outer Join between the Employee and Departments tables on the EmpID column. The result includes all matching rows between the tables, as well as any unmatched rows with NULL values.

SQL Left Outer Join

In a SQL Left Outer Join, we get the output of the matching rows between both tables. If no records match from the left table, those records are also included in the result set with NULL values.

SELECT * 
FROM Employee 
LEFT OUTER JOIN Departments 
ON Employee.EmpID = Departments.EmpID;

In the above query, we perform a Left Outer Join between the Employee and Departments tables. The result includes all matching rows between the tables, as well as any unmatched rows from the left table with NULL values.

SQL Right Outer Join

In a SQL Right Outer Join, we get the output of the matching rows between both tables. If no records match from the right table, those records are also included in the result set with NULL values.

SELECT * 
FROM Employee 
RIGHT OUTER JOIN Departments 
ON Employee.EmpID = Departments.EmpID;

In the above query, we perform a Right Outer Join between the Employee and Departments tables. The result includes all matching rows between the tables, as well as any unmatched rows from the right table with NULL values.

The Union between SQL Left Outer Join and SQL Right Outer Join

We can also combine the results of a SQL Left Outer Join and a SQL Right Outer Join using the UNION operator to achieve the same result as a SQL Full Outer Join.

SELECT * 
FROM Employee 
LEFT OUTER JOIN Departments 
ON Employee.EmpID = Departments.EmpID 
UNION ALL 
SELECT * 
FROM Employee 
RIGHT OUTER JOIN Departments 
ON Employee.EmpID = Departments.EmpID;

In the above query, we first perform a Left Outer Join and then a Right Outer Join. The UNION ALL operator combines the results of both joins, giving us the output of a SQL Full Outer Join.

Conclusion

In this article, we have explored the SQL Outer Join and its types, including the SQL Full Outer Join, SQL Left Outer Join, and SQL Right Outer Join. Understanding these join types is essential when working with multiple tables in SQL Server. By using the appropriate join type, we can retrieve the required data from the tables and represent it in a user-friendly way. We hope you found this article helpful in understanding the concepts of SQL Outer Join in SQL Server.