Cool! This works well. Here is the modified (few compilation issues rectified) and tested version.

;WITH Cte_Src AS (

SELECT

Db_name(database_id) databasename

,Max(x.Last_Date) Last_Access_time

,Getdate() curr_time

FROM

sys.dm_db_index_usage_stats

CROSS APPLY(VALUES(last_user_update)

,(last_user_lookup)

,(last_user_scan)

,(last_user_seek)) x (last_date)

WHERE last_date IS NOT NULL

AND Db_name(database_id) NOT IN ('msdb','master','tempdb')

GROUP BY database_id

)

MERGE master..AuditTable AS tgt

USING Cte_Src AS src

ON tgt.databasename = src.databasename

WHEN MATCHED AND src.Last_Access_time != tgt.Last_Access_time

THEN

UPDATE SET

tgt.last_access_time = src.last_access_time

, tgt.no_of_days = DateDiff(d,src.last_access_time, src.curr_time)

, tgt.last_upd_dtm = src.curr_time

WHEN NOT MATCHED BY TARGET

THEN INSERT (DatabaseName,last_access_time,no_of_days,last_upd_dtm)

VALUES ( src.DatabaseName,src.last_access_time,DateDiff(d,src.last_access_time, src.curr_time),GETDATE());

Thanks!