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