What is the full name of the actor who starred in most movies?
full name refers to first_name, last_name; actor who starred in the most movies refers to actor_id where Max(Count(film_id))
SELECT T.first_name, T.last_name FROM ( SELECT T2.first_name, T2.last_name, COUNT(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