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