What is the difference between the number of children's films and action films?
'children' AND 'action' are names of a category; Calculation = SUBTRACT(AVG('children'), AVG('action'))
SELECT SUM(IIF(T2.name = 'Children', 1, 0)) - SUM(IIF(T2.name = 'Action', 1, 0)) AS diff FROM film_category AS T1 INNER JOIN category AS T2 ON T1.category_id = T2.category_id