SQL 分组内求最大N个或最小N个

题目描述

   表 Employee

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
| 5  | Janet | 69000  | 1            |
| 6  | Randy | 85000  | 1            |
+----+-------+--------+--------------+

表 Department

+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

要求每个部门员工中挣得所在部门前三的工资，由于有多人可能工资一样，故每个部门求出的人数可能大于3
结果如下：

+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| IT         | Randy    | 85000  |
| IT         | Joe      | 70000  |
| Sales      | Henry    | 80000  |
| Sales      | Sam      | 60000  |
+------------+----------+--------+

SQL语句

select a.Name as Department,b.Name as Employee,b.Salary from
Department a 
join 
(select * from Employee e1 where (select 
count(distinct Salary) from Employee e2 where e2.Salary>e1.Salary 
and e1.DepartmentId=e2.DepartmentId)<3) b 
on b.DepartmentId=a.Id 
order by a.Id,b.Salary desc;

#查出每个部门中工资是前三水平的员工
select * from Employee e1 
where 
(select count(distinct Salary) from Employee e2 where e2.Salary>e1.Salary and e1.DepartmentId=e2.DepartmentId)
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