How many more "buffets" than "gyms" in Yelp business?
buffets refers to category_name = 'Buffets'; gyms refers to category_name = 'Gyms'; difference = SUBTRACT(SUM(category_name = 'Buffets'), SUM(category_name = 'Gyms'));
SELECT SUM(CASE WHEN T1.category_name LIKE 'Buffets' THEN 1 ELSE 0 END) - SUM(CASE WHEN T1.category_name LIKE 'Gyms' THEN 1 ELSE 0 END) FROM Categories AS T1 INNER JOIN Business_Categories AS T2 ON T1.category_id = T2.category_id