A date datatype does not contain milliseconds. A timestamp datatype stores fractional seconds. If you are using dates you'll have to convert them to timestamp datatypes.
However, if you are using timestamps, try this:
create table ts_info ( ts1 timestamp ) / insert into ts_info (ts1) values (systimestamp) / commit / select ts1, to_char(ts1, 'YYYY-MM-DD HH24:MI:SS.FF') from ts_info /
This was first published in June 2005