Oracle 12c中文亂碼，修改字符集的方法

在windows 7 64位上安裝Oracle 12c沒有設定字符集，採用的是操做系統默認字符集：WE8MSWIN1252，將字符集修改成：ZHS16GBK。因爲過程不可逆，首先須要備份數據庫。
1.數據庫全備

2.查詢當前字符集

SQL> select * from nls_database_parameters where parameter='NLS_CHARACTERSET';
PARAMETER                                VALUE
---------------------------------------- ----------------------------------------
NLS_CHARACTERSET                         WE8ISO8859P1

 3.關閉數據庫

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.

 4.啓動數據庫到mount狀態

SQL> startup mount
ORACLE instance started.
Total System Global Area  205520896 bytes
Fixed Size                  1266608 bytes
Variable Size             100666448 bytes
Database Buffers          100663296 bytes
Redo Buffers                2924544 bytes
Database mounted.

 5.限制session

SQL> alter system enable restricted session;
System altered.

6.查詢相關參數並修改

SQL> show parameter job_queue_processes;  
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
job_queue_processes                  integer     10

SQL> show parameter aq_tm_processes; 
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
aq_tm_processes                      integer     0

SQL> alter system set job_queue_processes=0;
System altered.

7.打開數據庫

SQL> alter database open;
Database altered.

8.修改字符集

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

出現錯誤提示，新字符集必須是老字符集的超集，也就原來字符集是新字符集的子集，能夠再Oracle官方文檔上查詢字符集包含關係。下面使用Oracle內部命令internal_use，跳過超集檢查，生產環境不建議使用此方法。

SQL> alter database character set internal_use ZHS16GBK;          
Database altered.

9.查詢當前字符集

SQL> select * from nls_database_parameters where parameter='NLS_CHARACTERSET';
PARAMETER                                VALUE
---------------------------------------- ----------------------------------------
NLS_CHARACTERSET                         ZHS16GBK

10.關閉數據庫

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.

11.啓動數據庫到mount狀態

SQL> startup mount
ORACLE instance started.
Total System Global Area  205520896 bytes
Fixed Size                  1266608 bytes
Variable Size             100666448 bytes
Database Buffers          100663296 bytes
Redo Buffers                2924544 bytes
Database mounted.

12.將相關參數改回原來值

SQL> alter system set job_queue_processes=10;
System altered.

13.打開數據庫

SQL> alter database open;
Database altered.