Database: customers_and_invoices
Question: Show all product names and the number of customers having an order on each product.
SQL:
SELECT T2.product_name ,  count(*) FROM Order_items AS T1 JOIN Products AS T2 ON T1.product_id  =  T2.product_id JOIN Orders AS T3 ON T3.order_id  =  T1.order_id GROUP BY T2.product_name