plsql 登入後提示：

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.

解決辦法：修改登錄檔

開啟登錄檔,‘開始’-‘執行’ 輸入‘regedit’-確定。

找到提示中給出的路徑，

找到 NLS_LANG 鍵，他的值原來是：SIMPLIFIED CHINESE_CHINA.ZHS16GBK

修改為：SIMPLIFIED CHINESE_CHINA.AL32UTF8

重新開啟plsql ，登入，好了。
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還有一種可能是由於安裝11g的時候沒選擇自定義安裝造成的

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.
這可是個麻煩事，不是改客戶端字符集的問題。要改資料庫的字符集：
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
提示我們的字符集：新字符集必須為舊字符集的超集，這時我們可以跳過超集的檢查做更改：
SQL> ALTER DATABASE character set INTERNAL_USE ZHS16GBK;
--我們看到這個過程和之前ALTER DATABASE CHARACTER SET操作的內部過程是完全相同的，也就是說INTERNAL_USE提供的幫助就是使Oracle資料庫繞過了子集與超集的校驗.
SQL> select * from v$nls_parameters;
SQL> shutdown immediate;
SQL> startup
SQL> select * from v$nls_parameters;
以後安裝oracle11g的時候記得選擇自定義安裝，把這個字符集的事情事先弄好