以下内容源自oracle documents -- Oracle8i National Language Support Guide
To change the database character set, perform the following steps. Not all of them are absolutely necessary, but they are highly recommended:
SQL> SHUTDOWN IMMEDIATE; -- or NORMAL
<do a full backup>
SQL> STARTUP MOUNT;
SQL> ALTER SYSTEM ENABLE RESTRICED SESSION;
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
SQL> ALTER DATABASE OPEN;
SQL> ALTER DATABASE CHARACTER SET <new_character_set_name>;
SQL> SHUTDOWN IMMEDIATE; -- or NORMAL
SQL> STARTUP;
To change the national character set, replace the ALTER DATABASE CHARACTER SET statement with ALTER DATABASE NATIONAL CHARACTER SET. You can issue both commands together if desired.
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 ;
SQL> SHUTDOWN IMMEDIATE; -- or NORMAL
SQL> STARTUP;