oracle数据表中的中文变问号

先查询一下select userenv('language') from dual;查看oracle字符集，

$ sqlplus /nolog

SQL> connect sys/oracle as sysdba

SQL> startup

如何设置ORACLE数据库的编码（ZHS16GBK）修改成UTF8

SQL> shutdown immediate;

SQL> startup mount;

SQL> alter system enable restricted session;

SQL> alter system set job_queue_processes=0;

SQL> alter database open;

SQL> alter database character set internal_use UTF8;

SQL> shutdown immediate;

SQL> startup;