oracle9204更改字符集步骤方法:
由于我们经常做不同数据库的导出导入时遇到的服务器的字符集不同，导致我们原有的无法正常导入工作，
这时需要我们做数据库字符集的更改工作，
字符集是在安装数据库时选定的，一旦数据库创建之后，数据库的字符集是不能改变的，如果要改变数据库的字符集，只有重新创建数据库。
但通常也可以在特定的条件下通过一些其他途径来完成字符集的转换（这里强烈建议创建数据库时就要考虑好字符集）
单字节=>单字节
多字节=>多字节
且是子集到超集时，可以用alter database CHARACTER set 新的字符集;
通常对于单字节向多字节转换和非子集到超集转换时采用exp/imp+internal_use的方法
这里只介绍AL32UTF8－>UTF8的步骤方法:
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检查当前的字符集为：
SQL> set wrap off
SQL> select * from v$nls_parameters;
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PARAMETER??????????????????????????????????????????????????????? VALUE
---------------------------- ---------------
NLS_LANGUAGE???????????????????????????????????????????????????? AMERICAN
NLS_TERRITORY??????????????????????????????????????????????????? AMERICA
NLS_CURRENCY???????????????????????????????????????????????????? $
NLS_ISO_CURRENCY???????????????????????????????????????????????? AMERICA
NLS_NUMERIC_CHARACTERS?????????????????????????????????????????? .,
NLS_CALENDAR???????????????????????????????????????????????????? GREGORIAN
NLS_DATE_FORMAT????????????????????????????????????????????????? DD-MON-RR
NLS_DATE_LANGUAGE??????????????????????????????????????????????? AMERICAN
NLS_CHARACTERSET???????????????????????????????????????????????? AL32UTF8
NLS_SORT???????????????????????????????????????????????????????? BINARY
NLS_TIME_FORMAT????????????????????????????????????????????????? HH.MI.SSXFF AM
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PARAMETER??????????????????????????????????????????????????????? VALUE
---------------------------- ---------------
NLS_TIMESTAMP_FORMAT???????????????????????????????????????????? DD-MON-RR HH.MI
NLS_TIME_TZ_FORMAT?????????????????????????????????????????????? HH.MI.SSXFF AM
NLS_TIMESTAMP_TZ_FORMAT????????????????????????????????????????? DD-MON-RR HH.MI
NLS_DUAL_CURRENCY??????????????????????????????????????????????? $
NLS_NCHAR_CHARACTERSET?????????????????????????????????????????? AL16UTF16
NLS_COMP???????????????????????????????????????????????????????? BINARY
NLS_LENGTH_SEMANTICS???????????????????????????????????????????? BYTE
NLS_NCHAR_CONV_EXCP????????????????????????????????????????????? FALSE
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19 rows selected.
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SQL>
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将数据库启动到RESTRICTED模式下做字符集更改：
SQL> conn /as sysdba? 注意这里，必须这样登陆，后面的shutdown and startup operation 才能成功
Connected.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
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Total System Global Area? 236000356 bytes
Fixed Size?????????????????? 451684 bytes
Variable Size???????????? 201326592 bytes
Database Buffers?????????? 33554432 bytes
Redo Buffers???????????????? 667648 bytes
Database mounted.
SQL> ALTER SYSTEM ENABLE RESTRICTED SESSION;
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System altered.
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SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
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System altered.
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SQL> ALTER SYSTEM SET AQ_TM_PROCESSES=0;
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System altered.
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SQL> alter database open;
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Database altered.
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SQL> ALTER DATABASE CHARACTER SET UTF8;
ALTER DATABASE CHARACTER SET UTF8
*
ERROR at line 1:
ORA-12712: new character set must be a superset of old character set
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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：
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SQL> ALTER DATABASE character set INTERNAL_USE UTF8;
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Database altered.
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SQL>ALTER DATABASE NATIONAL CHARACTER SET INTERNAL_USE UTF8;
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Database altered.
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SQL> select * from v$nls_parameters;
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PARAMETER??????????????????????????????????????????????????????? VALUE
---------------------------- ---------------
NLS_LANGUAGE???????????????????????????????????????????????????? AMERICAN
NLS_TERRITORY??????????????????????????????????????????????????? AMERICA
NLS_CURRENCY???????????????????????????????????????????????????? $
NLS_ISO_CURRENCY???????????????????????????????????????????????? AMERICA
NLS