Calculate how many percent of sales in North America is higher than the average sale per region for platform ID 9577.
in North America refers to region_name = 'North America'; platform ID 9577 refers to game_platform_id = 9577; percent = divide(subtract(num_sales where region_name = 'North America' and game_platform_id = 9577, avg(num_sales)), avg(num_sales)) * 100%
SELECT (SUM(CASE WHEN T2.region_name = 'North America' THEN T1.num_sales ELSE 0 END) - AVG(T1.num_sales)) * 100.0 / AVG(T1.num_sales) FROM region_sales AS T1 INNER JOIN region AS T2 ON T1.region_id = T2.id WHERE T1.game_platform_id = 9577