部分内容，收集自网络。

 一、查看用户

1.查看所有用户：
select * from dba_users;
select * from all_users;
select * from user_users;     

二、查看角色

1.当前用户被激活的全部角色  SESSION_ROLES describes the roles that are currently enabled to the user.
  select * from session_roles;

2.当前当前用户被授予的角色 USER_ROLE_PRIVS describes the roles granted to the current user.
  select * from user_role_privs;

3.全部用户被授予的角色 。DBA_ROLE_PRIVS describes the roles granted to all users and roles in the database.
  select * from dba_role_privs;

4、查看某个用户所拥有的角色    

select * from dba_role_privs where grantee='用户名';

5、查看某个角色所拥有的权限 DBA_SYS_PRIVS describes system privileges granted to users and roles.

select * from dba_sys_privs where grantee='CONNECT';

6.查看所有角色  DBA_ROLES describes all roles in the database.
  select * from dba_roles;

三、查看权限

1.基本权限查询：
select * from session_privs;   --SESSION_PRIVS describes the privileges that are currently available to the user.
select * from user_sys_privs;
select * from user_tab_privs;-- USER_TAB_PRIVS describes the object grants for which the current user is the object owner, grantor, or grantee
select * from dba_sys_privs ;
select * from role_sys_privs;--ROLE_SYS_PRIVS describes system privileges granted to roles. Information is provided only about roles to which the user has access.

2. 查看用户的系统权限(直接赋值给用户或角色的系统权限)

select * from dba_sys_privs;

select * from user_sys_privs;

2.查看用户的对象权限：
 select * from dba_tab_privs;
 select * from all_tab_privs;
 select * from user_tab_privs;

3.查看哪些用户有sysdba或sysoper系统权限(查询时需要相应权限)
  select * from v$pwfile_users;

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