本文目的：
研究common user要在不同的pdb间切换所需具有的权限；
研究common user在cdb上查询container_data_objects时如何限制其只能访问到某几个pdb对应的信息或者在某个特定的container_data_object对象上限制其只能访问到某几个pdb对应的信息，common user一般都有比较大的权限，但有的时候我们不想让common user通过cdb里的视图去访问到某些pdb的信息
先解释一下container_data_object的概念：Dba_table、dba_views中container_data=’Y’对应的表或视图，因为这些视图中包含了来自不同pdb的信息，所以被称作container_data_object
1、 只有common user才能使用alter session set container=PDBX在各个pdb间进行切换，前提是这个common user必须在这些pdb里至少具有create session 和 set container权限：
---在cdb里创建一个common user，赋予create session权限
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> create user c##guser2 identified by 773946 container=all;
User created.
SQL> grant create session to c##guser2;
Grant succeeded.
---以刚创建的c##guser2用户登陆cdb，set container到orapdba提示权限不足
oracle@ora12c1:/home/oracle>sqlplus c##guser2/773946
SQL*Plus: Release 12.1.0.1.0 Production on Thu Dec 12 21:22:44 2013
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options
SQL> alter session set container=orapdba;
ERROR:
ORA-01031: insufficient privileges
--[C1] -在orapdba里，grant set container权限给c##guser2
SQL> show con_name
CON_NAME
------------------------------
ORAPDBA
SQL> grant set container,create session to c##guser2;
Grant succeeded.
--- set container到orapdba成功
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> alter session set container=orapdba;
Session altered.
结论：common user用户要在不同的pdb间实现切换，必须在这些pdb上拥有create session和set container的权限，最简单的方法是在cdb上执行grant create session,set container to c##guser2 container=all进行全局的赋权
2、 通过alter user中的container_data_clause 进行container_data_objects访问权限控制：
---全局授权c##guser2查询系统视图的权限
SQL> grant select_catalog_role to c##guser2 container=all;
Grant succeeded.
---[C2] 以c##guser2登陆cdb$root查询cdb_data_files、v$session两个视图的内容
SQL> show user
USER is "C##GUSER2"
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> select distinct con_id from v$session;
CON_ID
----------
1
0
SQL> select distinct con_id from cdb_data_files;
CON_ID
----------
1
---开放给c##guser2用户查询特定pdb上信息的权限
SQL> show user
USER is "SYS"
SQL> show con_name
CON_NAME
------------------------------
CDB$ROOT
SQL> alter user c##guser2 set container_data=(CDB$root[C3] ,orapdba,orapdbb) container=current;
User altered.
---查询cdb_container_data可以看到c##guser2用户具有在部分pdb上查询container_data_object的权限
select * from CDB_container_data where username='C##GUSER2';
Grant succeeded.
---再次以c##guser2登陆cdb$root查询cdb_data_files、v$session两个视图的内容，能查到除了0、1之外的其它pdb的信息了
SQL> select distinct con_id from v$session;
CON_ID
----------
1
4
3
0
SQL> select distinct con_id from cdb_data_files;
CON_ID
----------
4
3
1
---对于v$session视图限制c##guser2只能访问orapdba相关的信息
SQL> alter user c##guser2 set container_data=(CDB$root,orapdba) for v$session container=current;
---cdb_container_data中又增加了两行基于特定对象的控制信息
select * from CDB_container_data where username='C##GUSER2'
---以c##guser2登陆Root查询cdb_data_files、v$session两个视图的内容，发现还是能查到con_id=4，即orapdbb的记录
SQL> select distinct con_id from v$session;
CON_ID
----------
1
4
3
0
SQL> select distinct con_id from cdb_data_files;
CON_ID
----------
4
3
1
---原因在于红色的部分还是生效的
---去除对于orapdbb的访问权限
SQL> alter user c##guser2 remove container_data=(orapdbb) container=current;
User altered.
---以c##guser2登陆Root查询cdb_data_files、v$session两个视图的内容，就不见了
con_id=4的记录
SQL> select distinct con_id from v$session;
CON_ID
----------
1
3
0
SQL> select distinct con_id from cdb_data_files;
CON_ID
----------
3
1
---对于v$session视图限制放宽让c##guser2也能访问orapdbb相关的信息
SQL> alter user c##guser2 add container_data=(orapdbb) for v$session
container=current;
User altered.
---以c##guser2登陆Root查询v$session视图又能看见con_id=4的记录，但
cdb_data_files里依然没有con_id=4的记录
User altered.
[C1]此处未授权create session也可以set container成功，实际操作时还是同时附上create session比较好