Employee 表包含所有员工信息，每个员工有其对应的工号 Id，姓名 Name，工资 Salary 和部门编号 DepartmentId 。

+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 85000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
| 5  | Janet | 69000  | 1            |
| 6  | Randy | 85000  | 1            |
| 7  | Will  | 70000  | 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，找出每个部门获得前三高工资的所有员工。例如，根据上述给定的表，查询结果应返回：

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

IT 部门中，Max 获得了最高的工资，Randy 和 Joe 都拿到了第二高的工资，Will 的工资排第三。销售部门（Sales）只有两名员工，Henry 的工资最高，Sam 的工资排第二。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/department-top-three-salaries
 

题解：通过前边SQL的练习，一气呵成的写完了这个大SQL

分析：1、查找每个部门工资的前三名：

        (select a.Id
from 
        Employee a
where
        (select count(distinct b.Salary)<=3
from 
         Employee b 
where 
         a.DepartmentId=b.DepartmentId
and  
         a.Salary<=b.Salary))

             2、对这些人进行降序排列：

select 
        Department.Name Department,Employee.Name Employee,Employee.Salary
from 
        Employee,Department
where 
        Employee.DepartmentId = Department.Id
and 
        Employee.Id
in
        符合条件的子查询：即分析一
order by 
         Employee.Salary desc;

结果：

完整代码：

select 
        Department.Name Department,Employee.Name Employee,Employee.Salary
from 
        Employee,Department
where 
        Employee.DepartmentId = Department.Id
and 
        Employee.Id
in
        (select a.Id
from 
        Employee a
where
        (select count(distinct b.Salary)<=3
from 
         Employee b 
where 
         a.DepartmentId=b.DepartmentId
and  
         a.Salary<=b.Salary))
order by 
         Employee.Salary desc;