NLS_DATE_LANGUAGEE和NLS_DATE_FORMAT

通过一道051的考题看这两个默认参数的用法：

91.View the Exhibit and examine the structure of the PROMOTIONS table. Which two SQL statements would execute successfully?

A.UPDATE promotions SET promo_cost = promo_cost+ 100 WHERE TO_CHAR(promo_end_date, 'yyyy') > '2000';
B.SELECT promo_begin_date FROM promotions WHERE TO_CHAR(promo_begin_date,'mon dd yy')='jul 01 98';
C.UPDATE promotions SET promo_cost = promo_cost+ 100 WHERE promo_end_date > TO_DATE(SUBSTR('01-JAN-2000',8));
D.SELECT TO_CHAR(promo_begin_date,'dd/month') FROM promotions WHERE promo_begin_date IN (TO_DATE('JUN 01 98'), TO_DATE('JUL 01 98'));
答案：AB
A:正确
B:正确
C:错误
D:错误
C和D的错误都是因为没有指定转换的格式，而默认的格式是通过

NLS_DATE_LANGUAGEE和NLS_DATE_FORMAT决定的，因此他们都存在问题，可以进行如下修改

SQL> select TO_DATE(SUBSTR('01-JAN-2000',8)) from dual;select TO_DATE(SUBSTR('01-JAN-2000',8)) from dualORA-01861: 文字与格式字符串不匹配SQL> alter session set NLS_DATE_FORMAT='yyyy';Session alteredSQL> select TO_DATE(SUBSTR('01-JAN-2000',8)) from dual;TO_DATE(SUBSTR('01-JAN-2000',8------------------------------2000/12/1SQL> select TO_DATE('JUN 01 98') from dual;select TO_DATE('JUN 01 98') from dualORA-01841: (完整) 年份值必须介于 -4713 和 +9999 之间, 且不为 0SQL> alter session set NLS_DATE_FORMAT='MON DD RR';Session alteredSQL> alter SESSION SET NLS_DATE_LANGUAGE='AMERICAN';Session alteredSQL> select TO_DATE('JUN 01 98') from dual;TO_DATE('JUN0198')------------------1998/6/1