select * from V$NLS_PARAMETERS;
SQL> alter session set NLS_DATE_LANGUAGE = 'SIMPLIFIED CHINESE';
Session altered
SQL> Select to_char(sysdate,'yyyy-Mon-day') from dual;
TO_CHAR(SYSDATE,'YYYY-MON-DAY'
------------------------------
2009-5月 -星期三
SQL> alter session set NLS_DATE_LANGUAGE='AMERICAN';
Session altered
SQL> Select to_char(sysdate,'yyyy-Mon-day') from dual;
TO_CHAR(SYSDATE,'YYYY-MON-DAY'
------------------------------
2009-May-wednesday
SQL>