Question: What percentage of films are horror films?
SQL: SELECT CAST(SUM(IIF(T2.name = 'Horror', 1, 0)) AS REAL) * 100 / COUNT(T1.film_id) FROM film_category AS T1 INNER JOIN category AS T2 ON T1.category_id = T2.category_id INNER JOIN film AS T3 ON T1.film_id = T3.film_id