How to take date time difference by milliseconds in Oracle

Question

In my requirement, I need to take the difference between date time by milliseconds. its most of the time receiving correctly, but in sometimes, it shows minus value.

in my table I'm storing EXPIREDDATE as follows, to update EXPIREDDATE time by 2 hours

UPDATE nd_user_encode_keys
SET EXPIREDDATE = SYSDATE + ( 1 / 1440 * 120)  -- here 120 means 2 hours

and according to my SP, above query running before the below query.

SELECT (EXPIRYDATETIME - SYSDATE) * 24 * 60 * 60 * 1000 as EXPIRYDATETIMEINMILISECONDS

My problem is most of the time result is 7200000 , but somtimes it shows minus value like this -34932000 . what could be the reason for this issue. can someone please explain.

Answer 1

When you have A - B , then the result can be:

• 0, if A = B
• a positive number, if A > B
• a negative number, if A < B --> that is your case

Why is expirydatetime less than sysdate and is that a valid value, I wouldn't know, but you should as it is your database, you're storing values into that table.

According to update statement you posted, and regarding the fact that sysdate won't return the same value "right now" as it did "a few moments ago", then it depends on when you ran that update .

Therefore, I presume it is about time difference between update and select .