Daily sql--statistics the total salary of employees in the past three months (excluding the latest month)

每日sql–Calculate the total salary of employees in the past three months（Excluding the latest month）

DDL

Create table If Not Exists Employee (Id int, Month int, Salary int);insert into Employee (Id, Month, Salary) values (1, 1, 20);insert into Employee (Id, Month, Salary) values (2, 1, 20);insert into Employee (Id, Month, Salary) values (1, 2, 30);insert into Employee (Id, Month, Salary) values (2, 2, 30);insert into Employee (Id, Month, Salary) values (3, 2, 40);insert into Employee (Id, Month, Salary) values (1, 3, 40);insert into Employee (Id, Month, Salary) values (3, 3, 60);insert into Employee (Id, Month, Salary) values (1, 4, 60);insert into Employee (Id, Month, Salary) values (3, 4, 70);

sql

select e1.Id,e1.month, case when  e1.salary is null then  0 else e1.salary end +case when  e2.salary is null then  0 else e2.salary end+case when  e3.salary is null then  0 else e3.salary end AS Salary
from 
(select Id,max(month)as month from Employee group by Id having count(1)>1) maxmonth
left join Employee e1 on e1.Id = maxmonth.Id and maxmonth.month >e1.month
left join Employee e2 on e2.Id = e1.Id and e2.month = e1.month-1
left join Employee e3 on e3.Id = e1.Id and e3.month = e1.month-2
ORDER BY e1.id ASC , e1.month DESC;