Who is the customer with the largest payment for rental films?
Who refers to first_name, last_name; the largest payment for rental refers to MAX(SUM(amount))
SELECT T.first_name, T.last_name FROM ( SELECT T1.first_name, T1.last_name, SUM(T2.amount) AS num FROM customer AS T1 INNER JOIN payment AS T2 ON T1.customer_id = T2.customer_id GROUP BY T1.first_name, T1.last_name ) AS T ORDER BY T.num DESC LIMIT 1