查看数据库当前字符集
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
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AMERICAN_AMERICA.WE8MSWIN1252
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将数据库置于restricted mode下
SQL> alter system enable restricted session;
System altered.
修改字符集到ZHS16GBK
SQL> ALTER DATABASE CHARACTER SET ZHS16GBK;
ALTER DATABASE CHARACTER SET ZHS16GBK
*
ERROR at line 1:
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;
ALTER DATABASE character set INTERNAL_USE ZHS16GBK
*
ERROR at line 1:
ORA-12721: operation cannot execute when other sessions are active
当前有连接处于active状态，kill掉session或者重启数据库。
SQL> shutdown immediate;
SQL> startup mount;
SQL> alter system enable restricted session;
System altered.
SQL> alter database open;
Database altered.
SQL> ALTER DATABASE character set INTERNAL_USE ZHS16GBK;
Database altered.
SQL> alter system disable restricted session;
System altered.
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
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AMERICAN_AMERICA.ZHS16GBK
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