List the names of all the publishers who published one game only.
name of publisher refers to publisher_name; published one game only refers to count(publisher_id) = 1
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 HAVING COUNT(DISTINCT T1.game_id) = 1 ) t