1.查看所有用户：

select * from dba_user;

select * from all_users;

select * from user_users;

2.查看用户系统权限：

select * from dba_sys_privs;

select * from all_sys_privs;

select * from user_sys_privs;

3.查看用户对象权限：

select * from dba_tab_privs;

select * from all_tab_privs;

select * from user_tab_privs;

4.查看所有角色：

select * from dba_roles;

5.查看用户所拥有的角色：

select * from dba_role_privs;

select * from user_role_privs;