When working with relational databases, JOIN operations are used to combine data from multiple tables based on a common column. The EXCEPT operator is one such operation which can be used to perform a JOIN with some additional functionality.

The EXCEPT operator is used to return the distinct rows from the left table that do not exist in the right table. In other words, it returns the difference between the two tables. This can be useful when you want to find records that are present in one table but not in another.

Let’s take a look at an example to understand how to use the EXCEPT operator in a JOIN operation. Suppose we have two tables - customers and orders.

Example Scenario

Table: customers

Table: orders

Now, let’s say we want to retrieve all the customers who have not placed any orders yet. We can accomplish this using the EXCEPT operator in a JOIN operation.

SQL Query

SELECT customers.customer_id, customers.customer_name
FROM customers
LEFT JOIN orders ON customers.customer_id = orders.customer_id
WHERE orders.customer_id IS NULL;

Explanation of the SQL query:

• We select the customer_id and customer_name columns from the customers table.
• We perform a LEFT JOIN between the customers and orders tables using the customer_id column as the join condition.
• We add a WHERE clause to filter out rows where orders.customer_id is NULL. This condition ensures that only customers who have not placed any orders are included in the result.

The result of the above query will be:

As you can see, the customer with customer_id 3 (Mike) is the only customer who hasn’t placed any orders.

The EXCEPT operator in combination with the JOIN operation provides a powerful way to find the difference between two tables. It can be used in various scenarios depending on your specific requirements.