Which publisher published the most games?
publisher refers to publisher_name; the most games refers to max(count(game_id))
SELECT T.publisher_name FROM ( SELECT T1.publisher_name, COUNT(DISTINCT T2.game_id) FROM publisher AS T1 INNER JOIN game_publisher AS T2 ON T1.id = T2.publisher_id GROUP BY T1.publisher_name ORDER BY COUNT(DISTINCT T2.game_id) DESC LIMIT 1 ) t