In MySQL, a full outer join, also known as a full join or full outer join, combines all rows from both the left and right tables based on a related column between them, and returns NULL for the columns where there is no matching row in either table. The basic syntax for a full outer join in MySQL is:
SELECT columns FROM table1 FULL OUTER JOIN table2 ON table1.column = table2.column;
However, MySQL does not have a built-in full outer join syntax. To achieve a full outer join in MySQL, we can use a combination of left and right joins with the UNION operator. Here’s an example:
SELECT orders.order_id, customers.customer_name FROM orders LEFT JOIN customers ON orders.customer_id = customers.customer_id UNION SELECT orders.order_id, customers.customer_name FROM orders RIGHT JOIN customers ON orders.customer_id = customers.customer_id WHERE orders.customer_id IS NULL;
In this example, we first perform a left join between the
orders table and the
customers table, which returns all orders and matching customer names. We then perform a right join between the same tables, but filter out any rows where there is a matching order ID, which returns all customers without a matching order ID. Finally, we combine the two results using the UNION operator to get a full outer join result.
For example, consider two tables,
departments, where the
departments table has a column
dept_id that relates to the
employees table’s column
dept_id. We can use a full outer join to get all the employees and departments, along with their corresponding department or employee names.
SELECT employees.employee_name, departments.department_name FROM employees LEFT JOIN departments ON employees.dept_id = departments.dept_id UNION SELECT employees.employee_name, departments.department_name FROM employees RIGHT JOIN departments ON employees.dept_id = departments.dept_id WHERE employees.employee_name IS NULL;