有学员提出了一个问题，

现象如下，难道SYSTEM比SYS用户的权限更大吗？

SYS@ora11g > grant select on v$session to lhr;

grant select on v$session to lhr

                *

ERROR at line 1:

ORA-02030: can only select from fixed tables/views

SYS@ora11g > conn system/lhr

Connected.

SYSTEM@ora11g > grant select on v$session to lhr;

Grant succeeded.

如果SYSTEM不能对V$SESSION赋权，那么请执行以下命令：

GRANT SELECT ON SYS.V_$SESSION TO SYSTEM WITH GRANT OPTION;

这样SYSTEM就可以对V$SESSION赋权了。

对于该问题可以从以下视图中获得答案：

SYS@ora11g > col OWNER format a10

SYS@ora11g > col object_name format a15

SYS@ora11g > SELECT d.owner,d.object_name,d.object_type FROM Dba_Objects d WHERE d.object_name IN  ( 'V$SESSION','V_$SESSION');

OWNER      OBJECT_NAME     OBJECT_TYPE

---------- --------------- -------------------

SYS        V_$SESSION      VIEW

PUBLIC     V$SESSION       SYNONYM

SYS@ora11g > SELECT d.owner,d.synonym_name,d.table_owner,d.table_name FROM DBA_SYNONYMS D WHERE D.synonym_name IN  ( 'V$SESSION','V_$SESSION');

OWNER      SYNONYM_NAME                   TABLE_OWNER                    TABLE_NAME

---------- ------------------------------ ------------------------------ ------------------------------

PUBLIC     V$SESSION                      SYS                            V_$SESSION

SYS@ora11g > SELECT D.OWNER,

  2         D.NAME,

  3         D.TYPE,

  4         D.REFERENCED_OWNER,

  5         D.REFERENCED_NAME,

  6         D.REFERENCED_TYPE

  7    FROM DBA_DEPENDENCIES D

  8   WHERE D.NAME IN ('V$SESSION', 'V_$SESSION');

OWNER      NAME          TYPE               REFERENCED_OWNER    REFERENCED_NAME   REFERENCED_TYPE

---------- ------------- ------------------ ------------------- ----------------- ------------------

PUBLIC     V$SESSION     SYNONYM            SYS                 V_$SESSION        VIEW

SYS        V_$SESSION    VIEW               SYS                 V$SESSION         VIEW

SYS@ora11g > SYS@ora11g > SELECT * FROM V$FIXED_TABLE d WHERE d.NAME IN ( 'V$SESSION','V_$SESSION','GV$SESSION');

NAME                            OBJECT_ID TYPE   TABLE_NUM

------------------------------ ---------- ----- ----------

GV$SESSION                     4294951258 VIEW       65537

V$SESSION                      4294950919 VIEW       65537

SYS@ora11g >

通过以上查询可以看到，V$SESSION属于公共同义词，它来源于SYS.V_$SESSION私有视图，而该视图又来源于系统底层表SYS.V$SESSION，而系统底层表SYS.V$SESSION又来源于系统底层表SYS.GV$SESSION。

Oracle选择访问对象的顺序原则是先SCHEMA后PUBLIC。所以，对于SYS用户而言，他查询V$SESSION视图其实是查询的系统底层表SYS.V$SESSION。对于系统底层表，是不能直接做赋权操作的。所以，SYS用户在将该视图赋权给其他用户的时候就会报错。而对于SYSTEM用户而言，他查询V$SESSION视图其实是查询的PUBLIC这个特殊用户下的公共同义词，而公共同义词是可以做赋权操作的。

& 说明：

有关Oracle同义词的更多内容介绍可以参考我的BLOG：http://blog.itpub.net/26736162/viewspace-2154285/

有关Oracle数据字典的更多内容可以参考我的BLOG：http://blog.itpub.net/26736162/viewspace-2153324/