How to Simulate a FULL OUTER JOIN in SQLite?

Simulating FULL OUTER JOIN in SQLite

SQLite natively supports INNER JOIN and LEFT JOIN operations, but it does not directly support FULL OUTER JOIN. To implement FULL OUTER JOIN behavior in SQLite, a user-defined query is required.

Solution

FULL OUTER JOIN can be implemented in SQLite using a combination of LEFT JOIN and UNION ALL operations. This approach involves performing two separate LEFT JOINs and combining the results using UNION ALL.

Code:

SELECT employee.*, department.*
FROM   employee 
       LEFT JOIN department 
          ON employee.DepartmentID = department.DepartmentID
UNION ALL
SELECT employee.*, department.*
FROM   department
       LEFT JOIN employee
          ON employee.DepartmentID = department.DepartmentID
WHERE  employee.DepartmentID IS NULL

Instructions:

The first LEFT JOIN obtains all employees and their corresponding department information. The second LEFT JOIN obtains all departments and their corresponding employee information. The UNION ALL operation combines the results of these two joins, effectively performing a FULL OUTER JOIN.

The WHERE clause in the second SELECT statement filters out employee records that are not associated with any department, ensuring a true FULL OUTER JOIN.

By using this technique, developers can perform FULL OUTER JOIN operations in SQLite even if SQLite itself does not support it.

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