How Can I Perform a FULL OUTER JOIN in SQLite?

Implementing full outer joins in SQLite

SQLite natively supports INNER JOIN and LEFT JOIN, but performing a FULL OUTER JOIN may make you worry about how to implement it. Fortunately, there is a solution to this problem.

Wikipedia Method

According to Wikipedia, full external connectivity can be achieved by following these steps:

1. Create two left joins: Create two left joins, one between the employee table and the department table (based on DepartmentID), the other between the department table and the employee table (also based on DepartmentID) .
2. Use UNION ALL: Use UNION ALL to combine the results of two left joins to collect records from the employee table and department table.
3. Filter NULL values: Apply the WHERE clause to identify records with NULL DepartmentID in the employees table. This ensures that the final result includes all sectors.

Code snippet

The following code snippet demonstrates this approach:

<code class="language-sql">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;</code>

With these steps, you can effectively perform a full external join in SQLite, ensuring you have a complete view of employee and department data.

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