Department Top Three Salaries

The Employee table holds all employees. Every employee has an Id, and there is also a column for the 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

The Department table holds all departments of the company.

Id	Name
1	IT
2	Sales

Write a SQL query to find employees who earn the top three salaries in each of the department. For the above tables, your SQL query should return the following rows.

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

描述

找出每个部门里 Salary 前三的人（可以并列）

代码

-- 方法一

select 
	Department.Name as Department, Employee.Name as Employee, Employee.Salary 
from 
	Employee inner join Department on Employee.DepartmentId = Department.Id 
where 
	3 > (
	select 
		count(distinct e.Salary) 
	from 
		Employee e 
	where 
		e.Salary > Employee.Salary and e.DepartmentId = Employee.DepartmentId
	) 
order by Employee.DepartmentId, Employee.Salary desc

-- 方法二

select 
	Department.Name as Department, e.Name as Employee, e.Salary 
from 
	Department, 
	(
	select 
		Employee.Name, 
		Employee.DepartmentId, 
		Employee.Salary, 
		@rank := (
			case 
				when @prevDept <> Employee.DepartmentId then 1 
				when @prevSalary = Employee.Salary then @rank 
				else @rank + 1 end
			) as rank, 
		@prevDept := Employee.DepartmentId, 
		@prevSalary := Employee.Salary 
	from 
		Employee, (select @rank := 0, @prevDept := 0, @prevSalary := 0) init 
	order by Employee.DepartmentId asc, Employee.Salary desc 
	) e
where Department.Id = e.DepartmentId and e.rank <= 3 
order by e.DepartmentId, e.Salary desc