--修改后重新啟動數(shù)據(jù)庫，永久生效
SQL> alter system set nls_date_format='yyyymmdd';
ERROR at line 1: --不能是memory scope（默認是both，所以也不行）
ORA-02096: specified initialization parameter is not modifiable with this option

SQL> alter system set nls_date_format='yyyymmdd' scope=spfile;
System altered.

SQL> show parameter nls_date_format? --這個時候還沒生效
NAME???????????????????????????????? TYPE??????? VALUE
------------------------------------ ----------- ------------------------------
nls_date_format????????????????????? string

--重啟數(shù)據(jù)庫后
SQL> show parameter nls_date_format
NAME???????????????????????????????? TYPE??????? VALUE
------------------------------------ ----------- ------------------------------
nls_date_format????????????????????? string????? yyyymmdd

SQL> select sysdate from dual;
SYSDATE
--------
20090627



--只對當前session有效，重登錄一次SQLPLUS，效果就消失了
SQL> alter session set nls_date_format='yyyy-mm-dd';?? --這個格式也很常用 yyyy-mm-dd hh:mi:ss
Session altered.? --同時會覆蓋初始化參數(shù)里的設置

SQL> select sysdate from dual;
SYSDATE
----------
2009-06-27