How do I calculate the time difference in milliseconds between two timestamps in Oracle?
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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 systimestamp - to_timestamp( '2012-07-23', 'yyyy-mm-dd' ) diff
6* from dual)
SQL> /
DAYS HOURS MINUTES SECONDS
---------- ---------- ---------- ----------
0 14 55 37.936
You can then convert each of those components into milliseconds and add them up
SQL> ed
Wrote file afiedt.buf
1 select extract( day from diff )*24*60*60*1000 +
2 extract( hour from diff )*60*60*1000 +
3 extract( minute from diff )*60*1000 +
4 round(extract( second from diff )*1000) total_milliseconds
5 from (select systimestamp - to_timestamp( '2012-07-23', 'yyyy-mm-dd' ) diff
6* from dual)
SQL> /
TOTAL_MILLISECONDS
------------------
53831842
Normally, however, it is more useful to have either the INTERVAL DAY TO SECOND representation or to have separate columns for hours, minutes, seconds, etc. rather than computing the total number of milliseconds between two TIMESTAMP values.