SELECT 
    ISNULL(DB_NAME(DATABASE_ID),'RESOURCEDB') AS DATABASENAME,
    CAST(COUNT(ROW_COUNT) * 8.0 /(1024.0) AS DECIMAL(28,2)) AS 'SIZE(MB)'
FROM SYS.dm_os_buffer_descriptors
GROUP BY database_id
ORDER BY DATABASENAME

SELECT SUM(single_pages_kb)+SUM(MULTI_PAGES_KB) FROM
(
    SELECT 
        SUM(single_pages_kb) AS single_pages_kb
        ,SUM(MULTI_PAGES_KB) AS MULTI_PAGES_KB        
    FROM SYS.dm_os_memory_clerks
    GROUP BY [TYPE]

    
) AS A 
UNION
SELECT COUNT(ROW_COUNT) * 8.0 FROM SYS.dm_os_buffer_descriptors