This document provides instructions for changing the character set of an Oracle database. It includes commands to: 1. Check the current character set settings using views like V$NLS_PARAMETERS 2. Shut down the database, mount it in restricted mode, and open it to prepare for changes 3. Use ALTER DATABASE commands to change the character set and national character set settings

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select * from v$NLS_PARAMETERS;
select * from nls_database_parameters where parameter ='NLS_CHARACTERSET';
select * from v$nls_parameters where PARAMETER like '%CHARACTERSET%';
select * from nls_session_parameters;
alter session set nls_date_format = 'yyyy/mm/dd hh24:mi:ss';
select distinct CLIENT_CHARSET from V$SESSION_CONNECT_INFO where
sid=sys_context('userenv','sid');
SQL> select * from v$nls_parameters where parameter='NLS_CHARACTERSET';
PARAMETER VALUE
-------------------- --------------------
NLS_CHARACTERSET TH8TISASCII
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SQL> select distinct OWNER, TABLE_NAME from DBA_TAB_COLUMNS where DATA_TYPE in
('NCHAR','NVARCHAR2', 'NCLOB');
SQL>SPOOL nlsnew.log
SQL>SHUTDOWN IMMEDIATE;
SQL>STARTUP MOUNT;
SQL> alter system enable restricted session;
SQL> alter system set job_queue_processes=0;
SQL> alter system set aq_tm_processes=0;
SQL> alter database open;
SQL> alter database amrims character set TH8TISASCII;
SQL> alter database amrims national character set UTF8;
SQL> shutdown immediate;
SQL> startup;
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1 SQL Plus --> connect sys/sys_password as sysdba
2 update props$
set value$ = 'TH8TISASCII'
where name = 'NLS_CHARACTERSET';
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--syntax
--ALTER DATABASE [<db_name>] CHARACTER SET <new_character_set>;
--ALTER DATABASE [<db_name>] NATIONAL CHARACTER SET <new_NCHAR_character_set>;
/*SQL> SHUTDOWN IMMEDIATE; -- or NORMAL
-- <do a full backup>
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 <new_character_set_name>;
SQL> SHUTDOWN IMMEDIATE; -- or NORMAL
SQL> STARTUP;
*/
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--Set NLS_CHARACTERSET
sqlplus / as sysdba;
SHUTDWON IMMEDIATE;
STARTUP MOUNT;
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER DATABASE OPEN;
ALTER DATABASE CHARACTER SET INTERNAL_USE TH8TISASCII; --this work
--ËÃ×Í ALTER DATABASE CHARACTER SET TH8TISASCII; --ãªéä´é㹡óշÕè set
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2. SHUTDWON IMMEDIATE;
STARTUP;
--Set NLS_CHARACTERSET, NLS_NCHAR_CHARACTERSET
sqlplus / as sysdba;
SHUTDWON IMMEDIATE;
STARTUP MOUNT;
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER DATABASE OPEN ;
UPDATE props$ SET value$='TH8TISASCII' WHERE name IN ('NLS_CHARACTERSET',
'NLS_NCHAR_CHARACTERSET');
commit;
SHUTDWON IMMEDIATE;
STARTUP;
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--Set NLS_CHARACTERSET áÅÐ Set NLS_CHARACTERSET, NLS_NCHAR_CHARACTERSET
sqlplus / as sysdba;
SHUTDWON IMMEDIATE;
STARTUP MOUNT;
ALTER SYSTEM ENABLE RESTRICTED SESSION;
ALTER DATABASE OPEN;
ALTER DATABASE CHARACTER SET INTERNAL_USE TH8TISASCII; --this work
UPDATE props$ SET value$='TH8TISASCII' WHERE name IN ('NLS_CHARACTERSET',
'NLS_NCHAR_CHARACTERSET');
commit;
SHUTDWON IMMEDIATE;
STARTUP;