Question: What are the top 10 customers' first and last names with the highest gross sales, and also what are the sales?
SQL: SELECT T1.first_name ,  T1.last_name ,  SUM(T2.total) FROM customers AS T1 JOIN invoices AS T2 ON T2.customer_id  =  T1.id GROUP BY T1.id ORDER BY SUM(T2.total) DESC LIMIT 10;