IN
The IN operator allows you to specify a list of possible values in the WHERE clause.
The IN operator is a shorthand for multiple OR conditions.
Example
SELECT * FROM customers
WHERE country IN ('Germany', 'France', 'UK');
NOT IN
By using the NOT keyword in front of the IN operator, you return all records that are NOT any of the values in the list.
Example
SELECT * FROM customers
WHERE country NOT IN ('Germany', 'France', 'UK');
IN (SELECT)
You can also use a SELECT statement inside the parenthesis to return all records that are in the result of the SELECT statement.
Example
SELECT * FROM customers
WHERE customer_id IN (SELECT customer_id FROM orders);
NOT IN (SELECT)
The result in the example above returned 89 records, that means that there are 2 customers that haven't placed any orders.
Let us check if that is correct, by using the NOT IN operator.
Example
SELECT * FROM customers
WHERE customer_id NOT IN (SELECT customer_id FROM orders);
