text: WITH may_rentals AS
  (
    SELECT
    	rental_id,
    	inventory_id
    FROM rental
    WHERE DATE(rental_ts) <= '2020-05-31'  
    AND DATE(rental_ts) >= '2020-05-01'
  ),
  film_count AS
  (
    SELECT 
    	inv.film_id, 
    	COUNT(rental_id) as rental_count
    FROM inventory inv
    LEFT JOIN may_rentals rnt
    ON rnt.inventory_id = inv.inventory_id
    GROUP BY film_id
  ),
  zero_rentals AS 
  (
    SELECT 
    	inv.film_id, 
    	inv.inventory_id,
    	rental_count
    FROM inventory inv
    JOIN film_count fc
    ON fc.film_id = inv.film_id
  )
  
  SELECT COUNT(1)
  FROM zero_rentals
  WHERE zero_rentals.rental_count = 0