The Oracle database stores all four digits of the year.
Oracle interprets the century depending on whether the YY or RR format is being used for two-digit year.
TRUNC(): truncate May 25, 2005, to the first day in the year
SQL>
SQL>
SQL> SELECT TRUNC(TO_DATE('25-MAY-2005'), 'YYYY') FROM dual;
TRUNC(TO_
---------
01-JAN-05
SQL>