在Oracle 12C中，账号分为两种，一种是公用账号，一种是本地账号（亦可理解为私有账号）。共有账号是指在CDB下创建，并在全部PDB中生效的账号，另一种是在PDB中创建的账号。
针对这两种账号的测试如下：
1.1 在PDB中创建测试账号
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$ROOT
结论：
如果在PDB中已经存在一个用户或者角色，则在CDB中不能创建相同的账号或者角色名。
1.2 在CDB中创建测试账号
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> create user C##GUIJIAN IDENTIFIED BY guijian; ------注意CDB中创建用户一定要带上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.
同样在CDB中创建账号后不能在PDB中出现同名的账号，因CDB中的账号对所有的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$ROOT
SQL> alter user sys identified by sys;
User altered.
SQL>
1.3 CDB下创建账号的权限问题
SQL> conn / as sysdba
Connected.
SQL> grant connect,create session to c##cdb;
Grant succeeded.
SQL> conn c##cdb/cdb@pdba
ERROR:
ORA-01045: user C##CDB lacks CREATE SESSION privilege; logon denied
Warning: You are no longer connected to ORACLE.
SQL> a
SP2-0004: Nothing to append.
SQL> conn / as sysdba
Connected.
SQL> alter session set container=pdba;
Session altered.
SQL> grant resource,connect to c##cdb;
Grant succeeded.
SQL> conn /as sysdba
Connected.
SQL> conn c##cdb/cdb@pdba
Connected.
SQL>
SQL> conn / as sysdba
Connected.
SQL> create user guijian identified by guijian container=current;
create user guijian identified by guijian container=current
*
ERROR at line 1:
ORA-65049: creation of local user or role is not allowed in CDB$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$ROOT
SQL> grant dba to c##guijian01 container=all;
Grant succeeded.
SQL> conn c##guijian01/guijian@pdba
Connected.
1.4 对象管理测试
对象管理测试中，我们简单测试在共有账号的数据对象的CDB和PDB下的不同。
1、在CDB下创建对象，在PDB下查看：
SQL> conn c##cdb/cdb
Connected.
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> create table cdb as select * from dba_users;
Table created.
SQL> commit;
Commit complete.
SQL>
可以看到，在CDB下的共有账号创建的对象在PDB下是看不到的。
2、在PDB下的共有账号创建对象,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，针对同一个共有账号在PDB下创建的账号在CDB是看不到的，此外我们还注意到一个细节，针对同一个共有账号，在PDB和CDB下创建的共有账号因在CDB和PDB下被赋予了不同的含义，故在CDB下创建的对象和在PDB下创建的对象是可以同名的，反之也成立。
结论：
1、 如果在PDB中已经存在一个用户或者角色，则在CDB中不能创建相同的账号或者角色名。
2、 同样在CDB中创建账号后不能在PDB中出现同名的账号，因CDB中的账号对所有的PDB都是有效的。
3、 在CDB中创建的账号将会在全部的PDB中出现，但是在CDB中的授权，如非特别指定的话，并不能传递到PDB中。
4、 针对同一个共有账号在PDB下创建的账号在CDB是看不到的。针对同一个共有账号，在PDB和CDB下创建的共有账号因在CDB和PDB下被赋予了不同的含义，故在CDB下创建的对象和在PDB下创建的对象是可以同名的，反之也成立。