What is the average rental rate of sci-fi film titles?
sci-fi film refers to category.name = 'Sci-Fi'; average rental rate = avg(rental_rate)
SELECT AVG(T1.rental_rate) FROM film AS T1 INNER JOIN film_category AS T2 ON T1.film_id = T2.film_id INNER JOIN category AS T3 ON T3.category_id = T2.category_id WHERE T3.`name` = 'Sci-Fi'