Show all product names and the number of customers having an order on each product.
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
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
[{'product_name': 'Arts', 'count(*)': 2}, {'product_name': 'Beer Menus', 'count(*)': 1}, {'product_name': 'Chocolate', 'count(*)': 1}, {'product_name': 'Fans', 'count(*)': 1}, {'product_name': 'Hard Drive', 'count(*)': 2}, {'product_name': 'Harry Potter 2', 'count(*)': 1}, {'product_name': 'Harry Potter 3', 'count(*)': 4}, {'product_name': 'Harry Potter 4', 'count(*)': 1}, {'product_name': 'Learning English', 'count(*)': 1}, {'product_name': 'TV', 'count(*)': 1}]