https://practicum.yandex.ru/trainer/sql-data-analyst/lesson/1739fbcf-17cf-48d0-bb4c-0a448cec10ab/task/ec31dab3-54af-44ad-8f89-498fe10c448f/

SELECT ct.name,
       AVG(m.length)
FROM movie AS m
LEFT OUTER JOIN film_category AS fc ON m.film_id = fc.film_id
LEFT OUTER JOIN category AS ct ON fc.category_id = ct.category_id
WHERE m.film_id IN (
                    SELECT mv.film_id
                    FROM movie AS mv
                    GROUP BY mv.film_id
                    ORDER BY SUM(mv.rental_rate) DESC
                    LIMIT 50)
GROUP BY ct.name
ORDER BY AVG(m.length) DESC;