Write SQL query to solve given problem: Calculate the difference between sales of games from region ID 2 and region ID 3.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(CASE WHEN T.region_id = 2 THEN T.num_sales ELSE 0 END) - SUM(CASE WHEN T.region_id = 3 THEN T.num_sales ELSE 0 END) FROM region_sales t