Database: superhero
Question: Which publisher created more superheroes: DC or Marvel Comics? Find the difference in the number of superheroes.
SQL: SELECT SUM(CASE WHEN T2.publisher_name = 'DC Comics' THEN 1 ELSE 0 END) - SUM(CASE WHEN T2.publisher_name = 'Marvel Comics' THEN 1 ELSE 0 END) FROM superhero AS T1 INNER JOIN publisher AS T2 ON T1.publisher_id = T2.id