How Can I Achieve a FULL OUTER JOIN in SQLite?

Implementing FULL OUTER JOIN in SQLite

SQLite is a commonly used database engine that provides a variety of connection operations, including INNER JOIN and LEFT JOIN. However, SQLite does not natively support FULL OUTER JOIN, which may pose some challenges.

Solution:

In order to perform FULL OUTER JOIN in SQLite, we can combine LEFT JOIN and UNION ALL. This method consists of three steps:

1. Perform LEFT JOIN between two tables to get all rows in the left table even if there are no matching rows in the right table.
2. Perform a LEFT JOIN between the same two tables, but this time swap the order of the tables to get all the rows in the right table even if there are no matching rows in the left table.
3. Use UNION ALL to combine the results of two LEFT JOINs to merge the rows in the two tables.

Example:

Consider the following two tables:

CREATE TABLE employee (EmployeeID INTEGER PRIMARY KEY, Name TEXT, DepartmentID INTEGER);
CREATE TABLE department (DepartmentID INTEGER PRIMARY KEY, Name TEXT);

To perform a FULL OUTER JOIN between these two tables, run the following query:

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;

This query will retrieve all rows in both employee and department tables, including those that have no matching rows in the other table.

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