Which game platform is the most popular in Europe?
game platform refers to game_platform_id; the most popular refers to max(num_sales); in Europe refers to region_name = 'Europe'
SELECT T.platform_name FROM ( SELECT T4.platform_name, SUM(T2.num_sales) FROM region AS T1 INNER JOIN region_sales AS T2 ON T1.id = T2.region_id INNER JOIN game_platform AS T3 ON T2.game_platform_id = T3.id INNER JOIN platform AS T4 ON T3.platform_id = T4.id WHERE T1.region_name = 'Europe' ORDER BY T2.num_sales DESC LIMIT 1 ) t