Answer : When you subtract two variables of type TIMESTAMP , you get an INTERVAL DAY TO SECOND which includes a number of milliseconds and/or microseconds depending on the platform. If the database is running on Windows, systimestamp will generally have milliseconds. If the database is running on Unix, systimestamp will generally have microseconds. 1 select systimestamp - to_timestamp( '2012-07-23', 'yyyy-mm-dd' ) 2* from dual SQL> / SYSTIMESTAMP-TO_TIMESTAMP('2012-07-23','YYYY-MM-DD') --------------------------------------------------------------------------- +000000000 14:51:04.339000000 You can use the EXTRACT function to extract the individual elements of an INTERVAL DAY TO SECOND SQL> ed Wrote file afiedt.buf 1 select extract( day from diff ) days, 2 extract( hour from diff ) hours, 3 extract( minute from diff ) minutes, 4 extract( second from diff ) seconds 5 from (select systimes...