Question #59 Out of Memory Error

I think this is the most efficient way to get the percentage of revenue for each of the following films: film_id <= 10 by its category. However, I get the "Out of Memory Error". I am trying to understand why the solution is MORE efficient than my codes. Can anyone please help? 

My solution: 

SELECT X.* FROM
(

SELECT distinct a.film_id, 
c.name AS category_name, 
SUM(f.amount) OVER (PARTITION BY a.film_id) *100.0/SUM(f.amount) OVER (PARTITION BY c.name) AS revenue_percent_category
FROM film a
INNER JOIN film_category b
ON a.film_id = b.film_id
INNER JOIN category c
ON b.category_id = c.category_id
INNER JOIN inventory d
ON b.film_id = d.film_id
INNER JOIN rental e
ON d.inventory_id = e.inventory_id
INNER JOIN payment f
ON e.rental_id = f.rental_id
ORDER BY a.film_id
) X
WHERE X.film_id <= 10

The answer: 

WITH movie_revenue AS (
    SELECT
        I.film_id, SUM(P.amount) revenue
    FROM payment P
    INNER JOIN rental R
    ON R.rental_id = P.rental_id
    INNER JOIN inventory I
    ON I.inventory_id = R.inventory_id    
    GROUP BY I.film_id
)
SELECT 
    MR.film_id, 
    C.name category_name,
    revenue * 100.0 / SUM(revenue) OVER(PARTITION BY C.name) revenue_percent_category
FROM movie_revenue MR
INNER JOIN film_category FC
  ON FC.film_id = MR.film_id
INNER JOIN category C
  ON C.category_id = FC.category_id
ORDER BY film_id
LIMIT 10
;