How is Oracle date implemented?

Question

How is Oracle date implemented? Is it stored as milliseconds or something like that?

Answer 1

An Oracle DATE stores the date and time to the second. An Oracle TIMESTAMP stores the date and time to up to 9 digits of subsecond precision, depending on the available hardware.

Both are implemented by storing the various components of the date and the time in a packed binary format. From the Oracle Concepts Guide section on dates

Oracle uses its own internal format to store dates. Date data is stored in fixed-length fields of seven bytes each, corresponding to century, year, month, day, hour, minute, and second.

You can use the DUMP() function to see the internal representation of any particular date (or any other value for that matter), but that's probably more than you need (or want) to know.

Answer 2

No. DATE is a timestamp value with seconds precision. You need TIMESTAMP(3) to store milliseconds.

Answer 3

Apparently, not in form of millisecs.

Which actually makes sense, since they do not have any running operations on current date/time:

http://www.ixora.com.au/notes/date_representation.htm

http://infolab.stanford.edu/~ullman/fcdb/oracle/or-time.html

http://www.akadia.com/services/ora_date_time.html