Oracle 12C -- plug unplugged PDB into CDB

connetct to CDB as a common user and verify that pdb_test is closed

SQL> select con_id,dbid,name,open_mode from v$pdbs;

    CON_ID       DBID NAME                           OPEN_MODE
---------- ---------- ------------------------------ ----------
           PDB$SEED                       READ ONLY
           PDB1                           READ ONLY
           P4                             READ ONLY
            PDB_TEST                       READ WRITE

SQL> alter pluggable database pdb_test close;
SQL> alter pluggable database pdb_test unplug into '/tmp/xmlfile1.xml';
SQL> select con_id,dbid,name,open_mode from v$pdbs;

    CON_ID       DBID NAME                           OPEN_MODE
---------- ---------- ------------------------------ ----------
           PDB$SEED                       READ ONLY
           PDB1                           READ ONLY
           P4                             READ ONLY
            PDB_TEST                       MOUNTED

A PDB must be dropped from the CDB before it can be plugged back into the same CDB

SQL> create pluggable database pdb_test using '/tmp/xmlfile1.xml' nocopy;
create pluggable database pdb_test using '/tmp/xmlfile1.xml' nocopy
*
ERROR at line :
ORA-: Pluggable database PDB_TEST already exists.

SQL> drop pluggable database pdb_test;
SQL> create pluggable database pdb_test using '/tmp/xmlfile1.xml' nocopy;
SQL> select con_id,dbid,name,open_mode from v$pdbs;

    CON_ID       DBID NAME                           OPEN_MODE
---------- ---------- ------------------------------ ----------
           PDB$SEED                       READ ONLY
           PDB1                           READ ONLY
           P4                             READ ONLY
            PDB_TEST                       MOUNTED

SQL> alter pluggable database pdb_test open;
SQL> select con_id,dbid,name,open_mode from v$pdbs;

    CON_ID       DBID NAME                           OPEN_MODE
---------- ---------- ------------------------------ ----------
           PDB$SEED                       READ ONLY
           PDB1                           READ ONLY
           P4                             READ ONLY
            PDB_TEST                       READ WRITE

SQL>