题目描述
Employee 表包含所有员工信息，每个员工有其对应的 Id, salary 和 department Id 。
+----+-------+--------+--------------+
| 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 |
+----+-------+--------+--------------+
Department 表包含公司所有部门的信息。
+----+----------+
| Id | Name |
+----+----------+
| 1 | IT |
| 2 | Sales |
+----+----------+
编写一个 SQL 查询，找出每个部门工资前三高的员工。例如，根据上述给定的表格，查询结果应返回：
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT | Max | 90000 |
| IT | Randy | 85000 |
| IT | Joe | 70000 |
| Sales | Henry | 80000 |
| Sales | Sam | 60000 |
+------------+----------+--------+
题目难度：困难
分析
工资前三高的员工可以通过连表求出来。
连表的条件：e1.DepartmentId = e2.DepartmentId and e1.Salary <= e2.Salary
再通过group by e1.Id having count(distinct e2.Salary) <= 3 求得前三高的员工
部门的名字也是通过连表求出来
连表的条件:e1.DepartmentId = d.Id
最后输出结果需要进行排序
order by d.Name, e1.Salary desc;
代码
# Write your MySQL query statement below
select
d.Name Department, e1.Name Employee, e1.Salary
from
Employee e1, Employee e2, Department d
where
e1.DepartmentId = e2.DepartmentId
and
e1.Salary <= e2.Salary
and
e1.DepartmentId = d.Id
group by
e1.Id
having
count(distinct e2.Salary) <= 3
order by
d.Name, e1.Salary desc
;
题目链接
https://leetcode-cn.com/problems/department-top-three-salaries/description/
