Question: Find the names of customers who have bought by at least three distinct products.
SQL: SELECT DISTINCT T1.customer_name FROM customers AS T1 JOIN customer_orders AS T2 ON T1.customer_id  =  T2.customer_id JOIN order_items AS T3 ON T2.order_id  =  T3.order_id GROUP BY T1.customer_id HAVING COUNT (DISTINCT T3.product_id)  >=  3