当遇到一个部门有多个员工记录，需要去取出每个部门薪水最少的那笔时，就可以用到分析函数row_number()拉
select * from(
select manager_id,employee_id,first_name,salary,row_number()
over(partition by manager_id order by salary) as currowid
from hr.employees)
where currowid = 1
博文来源：http://blog.csdn.net/huanghui22/archive/2007/04/23/1576119.aspx