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今天在练习TO_DATE()和TO_CHAR()函数的时候发现了一个问题,就是说nls_date_format参数在会话级alter session修改起作用,可在系统级alter system却不起作用.具体情况如下:
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- SQL> select sysdate from dual;
- SYSDATE
- ---------------
- 19-OCT-09
- SQL> alter session set nls_date_format="MON-DD-YYYY";
- Session altered.
- SQL> select sysdate from dual;
- SYSDATE
- -----------------
- OCT-19-2009
- SQL>
- ========================================================
- SQL> alter system set nls_date_format="MON-DD-YYYY" scope=spfile;
- System altered.
- SQL> shutdown immediate
- Database closed.
- Database dismounted.
- ORACLE instance shut down.
- SQL> startup
- ORACLE instance started.
- Total System Global Area 176160768 bytes
- Fixed Size 1247948 bytes
- Variable Size 92276020 bytes
- Database Buffers 79691776 bytes
- Redo Buffers 2945024 bytes
- Database mounted.
- Database opened.
- SQL> show parameter date
- NAME TYPE VALUE
- ------------------------------------ ----------- ------------------------------
- fixed_date string
- nls_date_format string MON-DD-YYYY
- nls_date_language string
- SQL> select sysdate from dual;
- SYSDATE
- ---------------
- 19-OCT-09
- SQL>
- 这个时候没有显示OCT-19-2009 而却是19-OCT-09
上网去搜了搜,找到了答案,那就是优先级的关系导致了这个问题.
系统级alter system的优先级低于会话级alter session的优先级,更加详细的情况接下来会演示出来.
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- nls参数、环境变量以及函数起作用的顺序如下(由低到高)
- instance级参数--->nls_lang--->session级参数--->函数
- C:>set nls_lang=SIMPLIFIED CHINESE_CHINA.ZHS16GBK
- C:>sqlplus / as sysdba
- SQL*Plus: Release 10.2.0.1.0 - Production on 星期三 7月 29 21:01:38 2009
- Copyright (c) 1982, 2005, Oracle. All rights reserved.
- 连接到:
- Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
- With the Partitioning, OLAP and Data Mining options
- SQL> show parameter nls_date_format
- NAME TYPE VALUE
- ------------------------------------ ----------- ------------------------------
- nls_date_format string yyyy/mm/dd hh24:mi:ss
- --很明显实例级别参数nls_date_format没有启作用
- SQL> select sysdate from dual;
- SYSDATE
- --------------
- 29-7月 -09
- --==============================
- --在注册表中清除nls_lang的值，这是我们发现实例级参数nls_date_format：格式
- yyyy/mm/dd hh24:mi:ss开始发挥作用
- SQL> exit
- 从 Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
- With the Partitioning, OLAP and Data Mining options 断开
- C:>sqlplus / as sysdba
- SQL*Plus: Release 10.2.0.1.0 - Production on Wed Jul 29 20:54:59 2009
- Copyright (c) 1982, 2005, Oracle. All rights reserved.
- ???:
- Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
- With the Partitioning, OLAP and Data Mining options
- SQL> select sysdate from dual;
- SYSDATE
- -------------------
- 2009/07/29 20:55:01
- --====================================
- --恢复注册表中的nls_lang设置：SIMPLIFIED CHINESE_CHINA.ZHS16GBK
- SQL> exit
- ? Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
- With the Partitioning, OLAP and Data Mining options ??
- C:>sqlplus / as sysdba
- SQL*Plus: Release 10.2.0.1.0 - Production on 星期三 7月 29 20:55:21 2009
- Copyright (c) 1982, 2005, Oracle. All rights reserved.
- 连接到:
- Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
- With the Partitioning, OLAP and Data Mining options
- SQL> select sysdate from dual;
- SYSDATE
- --------------
- 29-7月 -09
- SQL> alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';
- 会话已更改。
- --显然session级别的nls_date_format发挥了作用
- SQL> select sysdate from dual;
- SYSDATE
- -------------------
- 2009-07-29 20:55:55
- --很显然函数发挥了作用
- SQL> select to_char(sysdate,'yyyy-mm-dd hh:mi:ss') from dual;
- TO_CHAR(SYSDATE,'YY
- -------------------
- 2009-07-29 09:10:01
- SQL>
这下就清楚了,呵呵.