在Oracle 12C中，賬號分為兩種，一種是公用賬號，一種是本地賬號（亦可理解為私有賬號）。共有賬號是指在CDB下創建，並在全部PDB中生效的賬號，另一種是在PDB中創建的賬號。
針對這兩種賬號的測試如下：
1.1 在PDB中創建測試賬號
SQL> alter session set container=pdb01;
Session altered.
SQL> select username from dba_users where username like 'GUI%';
no rows selected
SQL> CREATE USER TEST IDENTIFIED BY test;
User created.
SQL> grant dba to test;
Grant succeeded.
SQL> show con_name
CON_NAME
------------------------------
PDB01
SQL> conn /as sysdba
Connected.
SQL> create user test identified by test;
create user test identified by test
*
ERROR at line 1:
ORA-65096: invalid common user or role name
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
結論：
如果在PDB中已經存在一個用戶或者角色，則在CDB中不能創建相同的賬號或者角色名。
1.2 在CDB中創建測試賬號
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> create user C##GUIJIAN IDENTIFIED BY guijian; ------注意CDB中創建用戶一定要帶上c##
User created.
SQL> create user c#gui identified by gui;
create user c#gui identified by gui
*
ERROR at line 1:
ORA-65096: invalid common user or role name
SQL> select username from dba_users where username like '%GUI%';
USERNAME
--------------------------------------------------------------------------------
C##GUIJIAN
SQL> ALTER SESSION SET CONTAINER=PDB01;
Session altered.
SQL> select username from dba_users where username like '%GUI%';
USERNAME
--------------------------------------------------------------------------------
C##GUIJIAN
SQL> create user guijian identified by guijian;
User created.
同樣在CDB中創建賬號后不能在PDB中出現同名的賬號，因CDB中的賬號對所有的PDB都是有效的。
SQL> create user c##guijian identified by guijian;
create user c##guijian identified by guijian
*
ERROR at line 1:
ORA-65094: invalid local user or role name
SQL> alter session set container=pdba;
Session altered.
SQL> show user
USER is "SYS"
SQL> alter user sys identified by sys;
alter user sys identified by sys
*
ERROR at line 1:
ORA-65066: The specified changes must apply to all containers
SQL> show con_name
CON_NAME
------------------------------
PDBA
SQL> conn /as sysdba
Connected.
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> alter user sys identified by sys;
User altered.
SQL>
1.3 CDB下創建賬號的權限問題
SQL> conn / as sysdba
Connected.
SQL> grant connect,create session to c##cdb;
Grant succeeded.
SQL> conn c##cdb/cdb@pdba
ERROR:
ORA-01045: user C##CDB lacks CREATE SESSION privilege; logon denied
Warning: You are no longer connected to ORACLE.
SQL> a
SP2-0004: Nothing to append.
SQL> conn / as sysdba
Connected.
SQL> alter session set container=pdba;
Session altered.
SQL> grant resource,connect to c##cdb;
Grant succeeded.
SQL> conn /as sysdba
Connected.
SQL> conn c##cdb/cdb@pdba
Connected.
SQL>
SQL> conn / as sysdba
Connected.
SQL> create user guijian identified by guijian container=current;
create user guijian identified by guijian container=current
*
ERROR at line 1:
ORA-65049: creation of local user or role is not allowed in CDB$ROOT
SQL> create user c##guijian identified by guijian container=current;
create user c##guijian identified by guijian container=current
*
ERROR at line 1:
ORA-65094: invalid local user or role name
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> create user c##guijian identified by guijian container=all;
User created.
SQL> create user c##guijian01 identified by guijian;
User created.
SQL> conn /as sysdba
Connected.
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> grant dba to c##guijian01;
Grant succeeded.
SQL> conn c##guijian01/guijian@pdba
ERROR:
ORA-01045: user C##GUIJIAN01 lacks CREATE SESSION privilege; logon denied
Warning: You are no longer connected to ORACLE.
SQL> conn /as sysdba
Connected.
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> grant dba to c##guijian01 container=all;
Grant succeeded.
SQL> conn c##guijian01/guijian@pdba
Connected.
1.4 對象管理測試
對象管理測試中，我們簡單測試在共有賬號的數據對象的CDB和PDB下的不同。
1、在CDB下創建對象，在PDB下查看：
SQL> conn c##cdb/cdb
Connected.
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> create table cdb as select * from dba_users;
Table created.
SQL> commit;
Commit complete.
SQL>
可以看到，在CDB下的共有賬號創建的對象在PDB下是看不到的。
2、在PDB下的共有賬號創建對象,在CDB下查看：
SQL> show con_name
CON_NAME
------------------------------
PDBA
SQL> show user
USER is "C##CDB"
SQL> select object_name from user_objects;
no rows selected
SQL> create table cdb as select * from dba_users;
Table created.
可以看出，針對同一個共有賬號在PDB下創建的賬號在CDB是看不到的，此外我們還注意到一個細節，針對同一個共有賬號，在PDB和CDB下創建的共有賬號因在CDB和PDB下被賦予了不同的含義，故在CDB下創建的對象和在PDB下創建的對象是可以同名的，反之也成立。
結論：
1、 如果在PDB中已經存在一個用戶或者角色，則在CDB中不能創建相同的賬號或者角色名。
2、 同樣在CDB中創建賬號后不能在PDB中出現同名的賬號，因CDB中的賬號對所有的PDB都是有效的。
3、 在CDB中創建的賬號將會在全部的PDB中出現，但是在CDB中的授權，如非特別指定的話，並不能傳遞到PDB中。
4、 針對同一個共有賬號在PDB下創建的賬號在CDB是看不到的。針對同一個共有賬號，在PDB和CDB下創建的共有賬號因在CDB和PDB下被賦予了不同的含義，故在CDB下創建的對象和在PDB下創建的對象是可以同名的，反之也成立。