How to Simulate a FULL OUTER JOIN in SQLite Using UNION ALL?

Simulate FULL OUTER JOIN in SQLite: use UNION ALL

SQLite does not natively support FULL OUTER JOIN. However, we can achieve the same effect by combining two LEFT JOINs and using UNION ALL.

Step 1: Create the left join base table

<code class="language-sql">SELECT employee.*, department.*
FROM employee LEFT JOIN department
ON employee.DepartmentID = department.DepartmentID</code>

Step 2: Create a null value inner join table

<code class="language-sql">SELECT employee.*, department.*
FROM department LEFT JOIN employee
ON employee.DepartmentID = department.DepartmentID
WHERE employee.DepartmentID IS NULL</code>

Step 3: Union all tables

Finally, combine the two LEFT JOIN tables using UNION ALL to create a FULL OUTER JOIN:

<code class="language-sql">SELECT *
FROM (
  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>

Note: UNION ALL does not remove duplicates, so the results may contain some duplicate values.

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