Which game has sold the fewest units?
which game refers to game_name; sold the fewest units refers to MIN(num_sales);
SELECT T.game_name FROM ( SELECT T1.game_name FROM game AS T1 INNER JOIN game_publisher AS T2 ON T1.id = T2.game_id INNER JOIN game_platform AS T3 ON T2.id = T3.game_publisher_id INNER JOIN region_sales AS T4 ON T3.id = T4.game_platform_id ORDER BY T4.num_sales LIMIT 1 ) t