Question: Which actor acted in the most films?
SQL: SELECT T.first_name, T.last_name FROM ( SELECT T2.first_name, T2.last_name, SUM(T1.film_id) AS num FROM film_actor AS T1 INNER JOIN actor AS T2 ON T1.actor_id = T2.actor_id GROUP BY T2.first_name, T2.last_name ) AS T ORDER BY T.num DESC LIMIT 1