When creating a database in a multitenant environment we must understand how character set works for CDB and PDBS.
In Oracle documentation we can find following lines
-When the character set of the CDB root is AL32UTF8, PDBs that are plugged into the CDB can have a different character set from the CDB root.
PDBs that you create from PDB$SEED inherit the AL32UTF8 character set from it, but you can migrate the PDB to a different character set.
-When the character set of the root is not AL32UTF8, all PDBs in the CDB use the character set of the CDB root.
Let’s see how it works. Suppose I have 2 non-CDB databases DB11G and DB12C and I want to migrate them in an Oracle 21c container.
As specified in the documentation we have to create a container with AL32UTF8 as character set. If not, we will not be able to create a PDB with AL32UTF8 as character set.
Ok so the first step is to create the CDB CDBPROD.
SQL> show con_name CON_NAME ------------------------------ CDB$ROOT SQL> select name from v$database; NAME --------- CDBPROD SQL> select value,parameter from NLS_DATABASE_PARAMETERS where PARAMETER like '%CHARACTERSET'; VALUE PARAMETER ----------------------------------- ----------------------------------- AL16UTF16 NLS_NCHAR_CHARACTERSET AL32UTF8 NLS_CHARACTERSET SQL>
And in this container CDBPROD let’s create the DB21UTF from seed
SQL> CREATE PLUGGABLE DATABASE DB21UTF ADMIN USER db21admin identified by root;
Pluggable database created.
SQL> alter pluggable database DB21UTF open;
Pluggable database altered.
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
4 DB21UTF READ WRITE NO
SQL>
And in DB21UTF the character set will be same as CDB$ROOT
SQL> alter session set container=DB21UTF; Session altered. SQL> show con_name; CON_NAME ------------------------------ DB21UTF SQL> select value,parameter from NLS_DATABASE_PARAMETERS where PARAMETER like '%CHARACTERSET'; VALUE PARAMETER ------------------------------ ------------------------------ AL16UTF16 NLS_NCHAR_CHARACTERSET AL32UTF8 NLS_CHARACTERSET SQL>
And then in DB21UTF, I can import data of DB11G.
But how can I create the PDB DB21ISO in CDBPROD with WE8ISO8859P15 as character set. One way is to
-create another CDB with the character set WE8ISO8859P15
-create the PDB DBISO in this new PDB
-Clone this DBISO in the CDBPROD
Ok let’s do that, below information of the new ISO CDB with the PDB
SQL> select name from v$database;
NAME
---------
CDBISO
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
3 DB21ISO READ WRITE NO
SQL> select value,parameter from NLS_DATABASE_PARAMETERS where PARAMETER like '%CHARACTERSET';
VALUE PARAMETER
------------------------------ ------------------------------
AL16UTF16 NLS_NCHAR_CHARACTERSET
WE8ISO8859P15 NLS_CHARACTERSET
SQL>
Now let’s clone DBISO in CDBPROD
On CDBISO let’s create a user we will use for a database link
SQL> show con_name CON_NAME ------------------------------ CDB$ROOT SQL> create user c##clone_user identified by root default tablespace users temporary tablespace temp container=ALL; User created. SQL> grant create session, create pluggable database, sysoper to c##clone_user container=ALL; Grant succeeded. SQL>
On CDBPROD let’s create a database link
Verify your TNS alias
oracle@oraadserver:/home/oracle/ [CDBPROD (CDB$ROOT)] tnsping cdbiso TNS Ping Utility for Linux: Version 21.0.0.0.0 - Production on 10-FEB-2022 15:44:03 Copyright (c) 1997, 2021, Oracle. All rights reserved. Used parameter files: /u01/app/oracle/network/admin/sqlnet.ora Used TNSNAMES adapter to resolve the alias Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = oraadserver)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = CDBISO))) OK (0 msec) oracle@oraadserver:/home/oracle/ [CDBPROD (CDB$ROOT)]
Create the dblink
SQL> select name from v$database; NAME --------- CDBPROD SQL> show con_name CON_NAME ------------------------------ CDB$ROOT SQL> create database link cloneiso connect to c##clone_user identified by root using 'CDBISO'; Database link created. SQL> select * from dual@cloneiso; D - X SQL>
And then clone the DBISO PDB in CDBPROD
SQL> select name from v$database; NAME --------- CDBPROD SQL> show con_name CON_NAME ------------------------------ CDB$ROOT SQL> create pluggable database DB21ISO from DB21ISO@cloneiso; Pluggable database created. SQL> alter pluggable database DB21ISO open; Pluggable database altered.
Now let’s verify the state of my PDBs in CDBPROD
SQL> select name from v$database;
NAME
---------
CDBPROD
SQL>
SQL> show pdbs
CON_ID CON_NAME OPEN MODE RESTRICTED
---------- ------------------------------ ---------- ----------
2 PDB$SEED READ ONLY NO
4 DB21UTF READ WRITE NO
7 DB21ISO READ WRITE NO
SQL>
Let’s verify the DB21ISO character set
SQL> select name from v$database; NAME --------- CDBPROD SQL> alter session set container=DB21ISO; Session altered. SQL> select value,parameter from NLS_DATABASE_PARAMETERS where PARAMETER like '%CHARACTERSET'; SQL> col value for a35 SQL> col parameter for a35 SQL> select value,parameter from NLS_DATABASE_PARAMETERS where PARAMETER like '%CHARACTERSET'; VALUE PARAMETER ----------------------------------- ----------------------------------- AL16UTF16 NLS_NCHAR_CHARACTERSET WE8ISO8859P15 NLS_CHARACTERSET SQL>
And the CDBPROD as seen before has AL32UTF8 as character set
SQL> conn / as sysdba Connected. SQL> select value,parameter from NLS_DATABASE_PARAMETERS where PARAMETER like '%CHARACTERSET'; VALUE PARAMETER ----------------------------------- ----------------------------------- AL16UTF16 NLS_NCHAR_CHARACTERSET AL32UTF8 NLS_CHARACTERSET SQL>
Conclusion
Always use AL32UTF8 for your CDB if possible, in this way you will be able to have PDBs with different character set
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