浅析NLS_SORT、NLS_COMP(-)

ORACLE数据库中，NLS_SORT和NLS_COMP参数控制着字符比较和排序的行为，如果配置不当，可能会使已有索引失去作用，从而影响数据库的性能。

首先，我们来看一下，可以通过哪些方式修改这两个参数。通过ALTER SESSION当然是没有问题了，那么通过环境变量是否可以那？实验如下：

[oracle@oadata ~]$ set | grep NLS
NLS_DATE_FORMAT='YYYY-MM-DD HH24:MI:SS'
NLS_LANG='SIMPLIFIED CHINESE_CHINA.AL32UTF8'
[oracle@oadata ~]$ 
[oracle@oadata ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on 星期三 9月 18 16:59:31 2013

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


连接到: 
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select parameter,value from nls_session_parameters;

PARAMETER		       VALUE
------------------------------ ------------------------------
NLS_LANGUAGE		       SIMPLIFIED CHINESE
NLS_TERRITORY		       CHINA
NLS_CURRENCY                   ￥
NLS_ISO_CURRENCY	       CHINA
NLS_NUMERIC_CHARACTERS	       .,
NLS_CALENDAR		       GREGORIAN
NLS_DATE_FORMAT 	       YYYY-MM-DD HH24:MI:SS
NLS_DATE_LANGUAGE	       SIMPLIFIED CHINESE
NLS_SORT		       BINARY
NLS_TIME_FORMAT 	       HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT	       DD-MON-RR HH.MI.SSXFF AM

PARAMETER		       VALUE
------------------------------ ------------------------------
NLS_TIME_TZ_FORMAT	       HH.MI.SSXFF AM TZR
NLS_TIMESTAMP_TZ_FORMAT        DD-MON-RR HH.MI.SSXFF AM TZR
NLS_DUAL_CURRENCY              ￥
NLS_COMP		       BINARY
NLS_LENGTH_SEMANTICS	       BYTE
NLS_NCHAR_CONV_EXCP	       FALSE

已选择17行。

SQL> 
SQL> exit
从 Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options 断开
[oracle@oadata ~]$ vi .bash_profile
[oracle@oadata ~]$ . .bash_profile
[oracle@oadata ~]$ set | grep NLS
NLS_COMP=LINGUISTIC
NLS_DATE_FORMAT='YYYY-MM-DD HH24:MI:SS'
NLS_LANG='SIMPLIFIED CHINESE_CHINA.AL32UTF8'
NLS_SORT=SCHINESE_PINYIN_M
[oracle@oadata ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on 星期三 9月 18 17:00:37 2013

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


连接到: 
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select parameter,value from nls_session_parameters;

PARAMETER		       VALUE
------------------------------ ------------------------------
NLS_LANGUAGE		       SIMPLIFIED CHINESE
NLS_TERRITORY		       CHINA
NLS_CURRENCY                   ￥
NLS_ISO_CURRENCY	       CHINA
NLS_NUMERIC_CHARACTERS	       .,
NLS_CALENDAR		       GREGORIAN
NLS_DATE_FORMAT 	       YYYY-MM-DD HH24:MI:SS
NLS_DATE_LANGUAGE	       SIMPLIFIED CHINESE
NLS_SORT		       SCHINESE_PINYIN_M
NLS_TIME_FORMAT 	       HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT	       DD-MON-RR HH.MI.SSXFF AM

PARAMETER		       VALUE
------------------------------ ------------------------------
NLS_TIME_TZ_FORMAT	       HH.MI.SSXFF AM TZR
NLS_TIMESTAMP_TZ_FORMAT        DD-MON-RR HH.MI.SSXFF AM TZR
NLS_DUAL_CURRENCY              ￥
NLS_COMP		       LINGUISTIC
NLS_LENGTH_SEMANTICS	       BYTE
NLS_NCHAR_CONV_EXCP	       FALSE

已选择17行。

SQL> 

由此可见，是可以通过环境变量来配置NLS_SORT 和NLS_COMP的（仅限于在session级别）。