Tell me the policy types of the customer named Selena Gerhold.
select * from customers as t1 join customer_policies as t2 on t1.customer_id = t2.customer_id where customer_details = "Selena Gerhold"
How about that of the customer named Sydnie Friesen?
select * from customers as t1 join customer_policies as t2 on t1.customer_id = t2.customer_id where customer_details = "Sydnie Friesen"
Tell me the details of the customers who do not have any policies.
select customer_details from customers except select t1.customer_details from customers as t1 join customer_policies as t2 on t1.customer_id = t2.customer_id