LeetCode--185.部门前三收入

建表

Create table If Not Exists Employee (Idint, Name varchar(255), Salary int, DepartmentId int);
Create table If Not Exists Department (Idint, Name varchar(255));
Truncate table Employee;
insert into Employee (Id, Name, Salary,DepartmentId) values ('1', 'Joe', '70000', '1');
insert into Employee (Id, Name, Salary,DepartmentId) values ('2', 'Henry', '80000', '2');
insert into Employee (Id, Name, Salary,DepartmentId) values ('3', 'Sam', '60000', '2');
insert into Employee (Id, Name, Salary,DepartmentId) values ('4', 'Max', '90000', '1');
insert into Employee (Id, Name, Salary,DepartmentId) values ('5', 'Janet', '69000', '1');
insert into Employee (Id, Name, Salary,DepartmentId) values ('6', 'Randy', '85000', '1');
Truncate table Department;
insert into Department (Id, Name) values('1', 'IT');
insert into Department (Id, Name) values('2', 'Sales');

开窗函数实现

select DISTINCT 
 (select `Name` from Department where Id = tmp.DepartmentId) Department,
 e.`Name`, e.Salary
 from Employee e, 
  (select DepartmentId, Salary, dense_rank() over(PARTITION by DepartmentId ORDER BY Salary desc) ranks from Employee ) tmp
 where e.Salary = tmp.Salary
 and tmp.ranks<=3
  ORDER BY Department, e.Salary desc

另一个做法：

select d.Name Department ,e1.Name Employee,e1.Salary Salary 
from Employee e1
inner join Department d on e1.DepartmentId= d.Id
where 3 >= (
           select count(distinct(e2.Salary)) from Employee e2 where e2.Salary >=e1.Salary and e2.DepartmentId=d.Id
       ) order by d.Name,e1.Salary Desc;