http://space.itpub.net/12778571/viewspace-624461
SQL> select name,value$ from props$ where name like '%NLS%';
NAME VALUE$
------------------------------ ------------------------------
NLS_LANGUAGE AMERICAN
NLS_TERRITORY AMERICA
NLS_CURRENCY $
NLS_ISO_CURRENCY AMERICA
NLS_NUMERIC_CHARACTERS .,
NLS_CHARACTERSET ZHS16GBK
NLS_CALENDAR GREGORIAN
NLS_DATE_FORMAT DD-MON-RR
NLS_DATE_LANGUAGE AMERICAN
NLS_SORT BINARY
NLS_TIME_FORMAT HH.MI.SSXFF AM
NAME VALUE$
------------------------------ ------------------------------
NLS_TIMESTAMP_FORMAT DD-MON-RR HH.MI.SSXFF AM
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
NLS_NCHAR_CHARACTERSET AL16UTF16
NLS_RDBMS_VERSION 10.2.0.1.0
20 rows selected.
NLS_CHARACTERSET是數據庫字符集，NLS_NCHAR_CHARACTERSET是國家字符集
ORACLE中有兩大類字符型數據，VARCHAR2是按照數據庫字符集來存儲數據。
而NVARCHAR2是按照國家字符集存儲數據的。同樣，CHAR和NCHAR也一樣，一是數據庫字符符，一是國家字符集。
轉換字符集，數據庫應該在RESTRICTED模式下
首先要確定修改後的字符集是不是修改前的超集，如果不是可能出現相同的代碼點對應不同的字符，出現亂碼的問題。
出現這個錯誤是 oracle 只支持從子集到超集的轉變
那有什麼方法可進行強制轉換呢？
該指令會跳過子集與超集的檢驗，當然強制轉換可能會造成數據的損壞，要謹慎使用!!
下面藉助eygle的帖子執行。
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 1845493760 bytes
Fixed Size 2021568 bytes
Variable Size 452986688 bytes
Database Buffers 1375731712 bytes
Redo Buffers 14753792 bytes
Database mounted.
SQL> alter session set sql_trace=true;
Session altered.
SQL> alter system enable restricted session;
System altered.
SQL> alter system set job_queue_processes=0;
System altered.
SQL> alter system set aq_tm_processes=0;
System altered.
SQL> alter database open;
Database altered.
SQL> alter database character set INTERNAL_USE UTF8;
Database altered.
SQL>update props$ set VALUE$='UTF8' where NAME='NLS_NCHAR_CHARACTERSET'
