To prepare for upgrading the PDB, use this procedure to unplug the PDB from the earlier release CDB.

1. Run the Pre-Upgrade Information Tool on the PDB.

   For example, where the PDB named salespdb is running in the CDB in $ORACLE_HOME_12.2:

   $ORACLE_HOME_12.2/jdk/bin/java -jar 
   $ORACLE_HOME_19/rdbms/admin/preupgrade.jar dir /tmp -c salespdb

2. Run preupgrade_fixups.sql on your source database.

   For example:

   CONNECT / AS SYSDBA
   SQL> ALTER SESSION SET CONTAINER=salespdb;
   
   SQL> @/tmp/preupgrade_fixups_salespdb.sql

3. Follow all recommendations listed in preupgrade.log.

4. Close the PDB you want to unplug.

   For example, use the following command to close the PDB salespdb:

   SQL> ALTER PLUGGABLE DATABASE salespdb CLOSE;
   

5. Log back in to CDB$ROOT:

   CONNECT / AS SYSDBA
   SQL> ALTER SESSION SET CONTAINER=CDB$ROOT;
   

6. Unplug the earlier release PDB using the following SQL command syntax, where pdb is the name of the PDB, and path is the location of the PDB XML file:

   ALTER PLUGGABLE DATABASE pdb UNPLUG INTO 'path/pdb.xml';

   For example, where the pdb name is salespdb and path is /home/oracle/salespdb.xml:

   SQL> ALTER PLUGGABLE DATABASE salespdb UNPLUG INTO '/home/oracle/salespdb.xml';
   

   The following response displays when the command is completed:

   Pluggable database altered

7. Drop the pluggable database salespdb, but keep data files.

   Oracle recommends that you drop salespdb after this procedure to clean up leftover information in the CDB views, and to help to avoid future issues. As a best practice guideline, back up your PDB in the destination CDB first, and then issue the DROP command on the source.

   Caution:

   After you drop the PDB from its original CDB, you cannot revert to it using previously taken backup, because the DROP command removes backup files.

   To drop the pluggable database, enter the following command:

   SQL> DROP PLUGGABLE DATABASE salespdb KEEP DATAFILES; 

8. Exit.