Here my goal is to change the default character set from WE8ISO8859P1 to AL32UTF8 on LINUX
Remember, this was tested on my DEVELOPMENT standalone database (refer Oracle Doc before doing on PROD).
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE 11.2.0.2.0 Production
TNS for Linux: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
SQL>
SQL> SELECT SUM (a.log_space + b.data_space + c.tempspace) "Total_DB_Size (G)"
FROM (SELECT ROUND (SUM (BYTES/1024/1024/1024), 2) data_space FROM dba_data_files) b,(SELECT ROUND (SUM (BYTES*members/1024/1024/1024), 2) log_space FROM v$log) a,
(SELECT NVL(ROUND(SUM(BYTES/1024/1024/1024),2), 0) tempspace FROM dba_temp_files) c;
Total_DB_Size (G)
-----------------
11.29
Do a full backup of the database because the ALTER DATABASE CHARACTER SET statement cannot be rolled back.
SQL> select name from v$database;
NAME
---------
TEST
SQL > select value from NLS_DATABASE_PARAMETERS where Parameter='NLS_CHARACTERSET';
VALUE
----------------------------------------
WE8ISO8859P1
SQL> SELECT VALUE FROM NLS_DATABASE_PARAMETERS WHERE PARAMETER='NLS_NCHAR_CHARACTERSET';
VALUE
----------------------------------------
AL16UTF16
SQL> select * from v$nls_parameters where parameter like '%CHARACTERSET';
PARAMETER
----------------------------------------------------------------
VALUE
----------------------------------------------------------------
NLS_CHARACTERSET
WE8ISO8859P1
NLS_NCHAR_CHARACTERSET
AL16UTF16
16UTF16
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
----------------------------------------------------
AMERICAN_AMERICA.WE8ISO8859P1
SQL> exit
$
$ expdp directory=TEST dumpfile=FULL_TEST_10112012.dmp logfile=FULL_TEST_10112012.log full=y
Full Database backup is taken,
SQL> select distinct(nls_charset_name(charsetid)) CHARACTERSET,
decode(type#, 1, decode(charsetform, 1, 'VARCHAR2', 2, 'NVARCHAR2','UNKOWN'),
9, decode(charsetform, 1, 'VARCHAR', 2, 'NCHAR VARYING', 'UNKOWN'),
96, decode(charsetform, 1, 'CHAR', 2, 'NCHAR', 'UNKOWN'),
112, decode(charsetform, 1, 'CLOB', 2, 'NCLOB', 'UNKOWN')) TYPES_USED_IN
from sys.col$ where charsetform in (1,2) and type# in (1, 9, 96, 112) order by CHARACTERSET;
CHARACTERSET TYPES_USED_IN
---------------------------------------- -------------
AL16UTF16 NCHAR
AL16UTF16 NCLOB
AL16UTF16 NVARCHAR2
WE8ISO8859P1 CHAR
WE8ISO8859P1 CLOB
WE8ISO8859P1 VARCHAR2
6 rows selected.
Oracle note suggests that if the character set conversion has happened between a 7/8 bit character set like WE8ISO8859P1, US7ASCII etc to a mutibyte character set like UTF8, AL32UTF8 etc,
then there will be data loss for clob columns which display the old character set.
So it is best to take a full back of the database, preferably using the tradional export utility.
SQL> ALTER DATABASE CHARACTER SET INTERNAL_USE AL32UTF8;
ALTER DATABASE CHARACTER SET INTERNAL_USE AL32UTF8
*
ERROR at line 1:
ORA-12719: operation requires database is in RESTRICTED mode
sql> shut immediate
SQL> startup Restrict
SQL> ALTER DATABASE CHARACTER SET INTERNAL_USE AL32UTF8;
Database altered.
after changing the character set bounced the database
SQL> select distinct(nls_charset_name(charsetid)) CHARACTERSET,
decode(type#, 1, decode(charsetform, 1, 'VARCHAR2', 2, 'NVARCHAR2','UNKOWN'),
9, decode(charsetform, 1, 'VARCHAR', 2, 'NCHAR VARYING', 'UNKOWN'),
96, decode(charsetform, 1, 'CHAR', 2, 'NCHAR', 'UNKOWN'),
112, decode(charsetform, 1, 'CLOB', 2, 'NCLOB', 'UNKOWN')) TYPES_USED_IN
from sys.col$ where charsetform in (1,2) and type# in (1, 9, 96, 112) order by CHARACTERSET;
CHARACTERSET TYPES_USED_IN
---------------------------------------- -------------
AL16UTF16 NCHAR
AL16UTF16 NCLOB
AL16UTF16 NVARCHAR2
AL32UTF8 CHAR
AL32UTF8 CLOB
AL32UTF8 VARCHAR2
6 rows selected.
SQL> select value from NLS_DATABASE_PARAMETERS where parameter='NLS_CHARACTERSET';
VALUE
--------------------------------------------------------------------------------
AL32UTF8
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
----------------------------------------------------
AMERICAN_AMERICA.AL32UTF8
SQL> SELECT VALUE FROM NLS_DATABASE_PARAMETERS WHERE PARAMETER='NLS_NCHAR_CHARACTERSET';
VALUE
--------------------------------------------------------------------------------
AL16UTF16
SQL> select * from v$nls_parameters where parameter like '%CHARACTERSET';
PARAMETER
----------------------------------------------------------------
VALUE
----------------------------------------------------------------
NLS_CHARACTERSET
AL32UTF8
NLS_NCHAR_CHARACTERSET
AL16UTF16
NOTE: we can use new GUI based DMU (Database Migration Assistant for Unicode) tool to convert the NLS_CHARACTERSET of an existing database to AL32UTF8 or UTF8
How to Migrate a WE8ISO8859P1 DB to AL32UTF8 using DMU 1.2 - an example (Doc ID 1546507.1)
