ALTER SESSION SET NLS_DATE_FORMAT = 'DD-MON-YY';
SELECT TO_DATE('20-DEC-07') FROM TABLE;
ORA-01843: месяц не верен.
ALTER SESSION SET NLS_DATE_FORMAT = 'MM-MON-YY';
SELECT TO_DATE('20-DEC-07', 'MM-MON-YY') FROM TABLE;
SELECT TO_DATE('20-Дек-07', 'DD-MON-YY') FROM TABLE;