角色在管理权限当中起到非常重要的作用，简化了权限授予的工作。
只需把对象的权限授予给角色，再把角色的权限授予给用户，这样不用直接把多对象的
权限授予多用户的繁杂。

----查看Scott用户拥有的角色： 

---权限使用举例：

--查看Scott用户应有的系统权限：

sys@PROD>desc dba_role_privs

 Name                                                              Null?    Type

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

 GRANTEE                                                                    VARCHAR2(30)

 GRANTED_ROLE                                                      NOT NULL VARCHAR2(30)

 ADMIN_OPTION                                                               VARCHAR2(3)

 DEFAULT_ROLE                                                               VARCHAR2(3)

sys@PROD>select GRANTEE,GRANTED_ROLE,DEFAULT_ROLE

  2  from dba_role_privs where grantee='SCOTT';

GRANTEE                        GRANTED_ROLE                   DEF

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

SCOTT                          RESOURCE                       YES

SCOTT                          WRUSER                         YES

SCOTT                          PLUSTRACE                      YES

---查看角色的系统权限：

sys@PROD>DESC role_sys_privs

 Name                                                              Null?    Type

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

 ROLE                                                              NOT NULL VARCHAR2(30)

 PRIVILEGE                                                         NOT NULL VARCHAR2(40)

 ADMIN_OPTION                                                               VARCHAR2(3)

sys@PROD>select * from role_sys_privs where role='RESOURCE';

ROLE                           PRIVILEGE                                ADM

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

RESOURCE                       CREATE TRIGGER                           NO

RESOURCE                       CREATE SEQUENCE                          NO

RESOURCE                       CREATE TYPE                              NO

RESOURCE                       CREATE PROCEDURE                         NO

RESOURCE                       CREATE CLUSTER                           NO

RESOURCE                       CREATE OPERATOR                          NO

RESOURCE                       CREATE INDEXTYPE                         NO

RESOURCE                       CREATE TABLE                             NO

8 rows selected.

---查看WRUSER角色的对象权限：
sys@PROD>col ROLE for a20
sys@PROD>col OWNER for a20
sys@PROD>col TABLE_NAME for a20
sys@PROD>col COLUMN_NAME for a10
sys@PROD>col PRIVILEGE for a15
sys@PROD>select ROLE,OWNER,TABLE_NAME,COLUMN_NAME,PRIVILEGE
  2  from role_tab_privs 
  3   where role ='WRUSER';


ROLE                 OWNER                TABLE_NAME           COLUMN_NAM PRIVILEGE
-------------------- -------------------- -------------------- ---------- ---------------
WRUSER               SYS                  MYTABLE                         UPDATE
WRUSER               SYS                  MYTABLE                         INSERT
WRUSER               SYS                  MYTABLE                         SELECT

------------------------------------------------
1 WRUSER SYS MYTABLE UPDATE
2 WRUSER SYS MYTABLE INSERT
3 WRUSER SYS MYTABLE SELECT