Percentage of IO for each database

WITH Agg_IO_Stats
AS
(
	SELECT 
		DB_NAME(database_id) AS database_name,
		CAST(sum(num_of_bytes_read + num_of_bytes_written) / 1048576 AS decimal(12,2)) AS io_in_mb
	FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS DM_IO_Stats
	GROUP BY database_id
)
SELECT
	ROW_NUMBER() over(ORDER BY io_in_mb DESC) AS row_num,
	database_name,
	io_in_mb,
	CAST(io_in_mb / SUM(io_in_mb) over() * 100 AS decimal(5,2)) AS pct
FROM Agg_IO_Stats
ORDER BY row_num;