ลูกค้ามีนโยบายประเภทใดบ้างที่มีนโยบายมากที่สุด?ไม่จำเป็นต้องใช้ตารางทั้งหมด
What are all the policy types of the customer that has the most policies listed?It is not neccessary to use all the tables.
 customers:  (customer_id [ VARCHAR ] customer_name [ VARCHAR) ]
SELECT DISTINCT t3.policy_type_code FROM customers AS t1 JOIN customers_policies AS t2 ON t1.customer_id = t2.customer_id JOIN available_policies AS t3 ON t2.policy_id = t3.policy_id WHERE t1.customer_name = (SELECT t1.customer_name FROM customers AS t1 JOIN customers_policies AS t2 ON t1.customer_id = t2.customer_id GROUP BY t1.customer_name ORDER BY COUNT(*) DESC LIMIT 1)