Question: List all the policy types used by the customer enrolled in the most policies.
SQL: 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)