Which customer has made the most orders? Show his/her full name.
most order refers to Max(Count(order_id)); customer refers to first_name, last_name
SELECT T1.first_name, T1.last_name FROM customer AS T1 INNER JOIN cust_order AS T2 ON T1.customer_id = T2.customer_id GROUP BY T1.first_name, T1.last_name ORDER BY COUNT(*) DESC LIMIT 1