nls_instance_parameter 中NLS_LANG是否受OS环境变量影响测试

nls_instance_parameters取值与v$system_parameter一致,下面让我们看一下v$system_parameter 在官方文档的定义：

V$SYSTEM_PARAMETER displays information about the initialization parameters that are currently in effect for the instance.

A new session inherits parameter values from the instance-wide values.

从这里，我们可知，nls_instance_parameters的值有参数文件决定，那么会不会受到环境变量的影响哪？经验证，是不会的！过程如下：

首先，我们来看一下NLS_LANGUAGE的取值

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sys>select parameter,value from nls_instance_parameters where parameter='NLS_LANGUAGE';          PARAMETER              VALUE  ------------------------------ ------------------------------  NLS_LANGUAGE               SIMPLIFIED CHINESE

关闭数据库，然后修改环境变量NLS_LANG:

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sys>shutdown immediate  Database closed.  Database dismounted.  ORACLE instance shut down.  sys>exit  Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production  With the Partitioning, OLAP, Data Mining and Real Application Testing options  [oracle@oadata ~]$ vi .bash_profile  [oracle@oadata ~]$ . .bash_profile  [oracle@oadata ~]$ set | grep NLS  NLS_DATE_FORMAT='YYYY-MM-DD HH24:MI:SS' NLS_LANG=AMERICAN_AMERICA.AL32UTF8

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[oracle@oadata ~]$ sqlplus / as sysdba          SQL*Plus: Release 11.2.0.3.0 Production on Wed Sep 18 16:01:00 2013          Copyright (c) 1982, 2011, Oracle.  All rights reserved.          Connected to an idle instance.          SQL> startup  ORACLE instance started.          Total System Global Area 2137886720 bytes  Fixed Size          2230072 bytes  Variable Size        1342179528 bytes  Database Buffers      788529152 bytes  Redo Buffers            4947968 bytes  Database mounted.  Database opened.  SQL> select parameter,value from nls_instance_parameters where parameter='NLS_LANGUAGE';          PARAMETER              VALUE  ------------------------------ ------------------------------  NLS_LANGUAGE               SIMPLIFIED CHINESE

可见，nls_instance_parameters只受参数文件的影响，而不受环境变量影响。

nls_session_parameters 它的查询结果默认会从nls_instance_parameters继承，但是如果，我们在环境变量或者通过ALTER SESSION 改变了nls的相关参数，则会覆盖默认值。

例如，当环境变量NLS_LANG=AMERICAN_AMERICA.AL32UTF8

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SQL> select parameter,value from nls_session_parameters where parameter='NLS_LANGUAGE';          PARAMETER              VALUE  ------------------------------ ------------------------------  NLS_LANGUAGE               AMERICAN

当环境变量NLS_LANG='SIMPLIFIED CHINESE_CHINA.AL32UTF8'

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SQL> select parameter,value from nls_session_parameters where parameter='NLS_LANGUAGE';          PARAMETER              VALUE  ------------------------------ ------------------------------  NLS_LANGUAGE               SIMPLIFIED CHINESE