List a sum of all the payments for all the customers.
select t2.first_name, t2.last_name, sum(t1.amount_payment) from customer_payments as t1 join customers as t2 on t1.customer_id = t2.customer_id group by t2.customer_id
How much in total has customer with first name as Carole and last name as Bernhard paid?
select sum(t1.amount_payment) from customer_payments as t1 join customers as t2 on t1.customer_id = t2.customer_id where t2.first_name = "Carole" and t2.last_name = "Bernhard"