Indicate, by region, which platform has sold the most games.
region refers to region_name; platform refers to game_platform; sold the most games refers to MAX(SUM(num_sales));
SELECT T.region_name FROM ( SELECT T1.platform_name, T4.region_name, SUM(T3.num_sales) FROM platform AS T1 INNER JOIN game_platform AS T2 ON T1.id = T2.platform_id INNER JOIN region_sales AS T3 ON T1.id = T3.game_platform_id INNER JOIN region AS T4 ON T3.region_id = T4.id GROUP BY T1.platform_name, T4.region_name ORDER BY SUM(T3.num_sales) DESC LIMIT 1 ) t