SYS AS SYSDBA@devcedb>select * from v$version;
BANNER
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Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
1）修改oracle的隐含参数"_enable_rename_user"
SYS AS SYSDBA@devcedb>alter system set "_enable_rename_user"=true scope=spfile;
System altered.
2)用restrict模式启动数据库
startup restrict force;
或者
alter system enable restricted session;
SYS AS SYSDBA@devcedb>alter system quiesce restricted;
System altered.
3）修改username
SYS AS SYSDBA@devcedb>alter user amber rename to ambernew identified by amber;
User altered.
4)disable restrict
SYS AS SYSDBA@devcedb>alter system disable restricted session;
System altered.
另外，在网上还有一种修改oracle数据字典的方法，并没有版本限制：
1)修改数据字典user$
update user$ set name='' where user#=''; --生产库更改数据字典请谨慎操作
2)手工生成检查点，使update操作写入数据文件
alter system checkpoint;
3)清除share pool，让oracle读更新后的数据字典
alter system flush shared_pool; --生产库flush sharepool请谨慎操作
user$作为oracle的核心基表之一，修改数据字典会不会造成系统不稳定产生ora-600错误等等都不好说，所以生产上一定要慎重。