What is the customer last name, id and phone number with most number of orders?
SELECT T2.customer_last_name ,  T1.customer_id ,  T2.phone_number FROM Orders AS T1 JOIN Customers AS T2 ON T1.customer_id  =  T2.customer_id GROUP BY T1.customer_id ORDER BY count(*) DESC LIMIT 1
customer with most number of orders refers to MAX(count(order_id)); customer last name, id, and phone number refers to customer_last_name, customer_id, and phone_number respectively; joining of Orders and Customers tables on customer_id to match records;