List the customers first and last name of 10 least expensive invoices.
SELECT T1.first_name ,  T1.last_name FROM customers AS T1 JOIN invoices AS T2 ON T2.customer_id  =  T1.id ORDER BY total LIMIT 10;
10 least expensive invoices refers to ORDER BY total ASC LIMIT 10; customers first and last name refers to T1.first_name, T1.last_name;