plsql 登录后提示：

Database character set (AL32UTF8) and Client character set (ZHS16GBK) are different.
Character set conversion may cause unexpected results.

Note: you can set the client character set through the NLS_LANG environment variable or the NLS_LANG registry key in
HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_OraClient11g_home2.

解决办法：修改注册表

打开注册表,‘开始’-‘运行’ 输入‘regedit’-确定。

找到提示中给出的路径，

找到 NLS_LANG 键，他的值原来是：SIMPLIFIED CHINESE_CHINA.ZHS16GBK

修改为：SIMPLIFIED CHINESE_CHINA.AL32UTF8

重新打开plsql ，登录，好了。
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还有一种可能是由于安装11g的时候没选择自定义安装造成的

Database character set (AL32UTF8) and Client character set (ZHS16GBK) are different.
Character set conversion may cause unexpected results.
Note: you can set the client character set through the NLS_LANG environment variable or the NLS_LANG registry key in
HKEY_LOCAL_MACHINE/SOFTWARE/ORACLE/KEY_OraDb11g_home

SIMPLIFIED CHINESE_CHINA.ZHS16GBK 包含 AMERICAN_AMERICA.AL32UTF8.
这可是个麻烦事，不是改客户端字符集的问题。要改数据库的字符集：
SQL> conn /as sysdba
SQL> shutdown immediate;
SQL> startup mount
SQL> ALTER SYSTEM ENABLE RESTRICTED SESSION;
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
SQL> ALTER SYSTEM SET AQ_TM_PROCESSES=0;
SQL> alter database open;
SQL> ALTER DATABASE CHARACTER SET ZHS16GBK;
ORA-12712: new character set must be a superset of old character set
提示我们的字符集：新字符集必须为旧字符集的超集，这时我们可以跳过超集的检查做更改：
SQL> ALTER DATABASE character set INTERNAL_USE ZHS16GBK;
--我们看到这个过程和之前ALTER DATABASE CHARACTER SET操作的内部过程是完全相同的，也就是说INTERNAL_USE提供的帮助就是使Oracle数据库绕过了子集与超集的校验.
SQL> select * from v$nls_parameters;
SQL> shutdown immediate;
SQL> startup
SQL> select * from v$nls_parameters;
以后安装oracle11g的时候记得选择自定义安装，把这个字符集的事情事先弄好