Write SQL query to solve given problem: What are the sales made by the games in Japan region?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(CASE WHEN T2.region_name = 'Japan' THEN T1.num_sales ELSE 0 END) AS nums FROM region_sales AS T1 INNER JOIN region AS T2 ON T1.region_id = T2.id