# 579.(Hard)查询员工的累计薪水

Employee 表保存了一年内的薪水信息。

请你编写 SQL 语句，对于每个员工，查询他除最近一个月（即最大月）之外，剩下每个月的近三个月的累计薪水（不足三个月也要计算）。

结果请按 Id 升序，然后按 Month 降序显示。

示例： 输入：

| Id | Month | Salary |
| -- | ----- | ------ |
| 1  | 1     | 20     |
| 2  | 1     | 20     |
| 1  | 2     | 30     |
| 2  | 2     | 30     |
| 3  | 2     | 40     |
| 1  | 3     | 40     |
| 3  | 3     | 60     |
| 1  | 4     | 60     |
| 3  | 4     | 70     |

输出：

| Id | Month | Salary |
| -- | ----- | ------ |
| 1  | 3     | 90     |
| 1  | 2     | 50     |
| 1  | 1     | 20     |
| 2  | 1     | 20     |
| 3  | 3     | 100    |
| 3  | 2     | 40     |

解释：

员工 '1' 除去最近一个月（月份 '4'），有三个月的薪水记录：月份 '3' 薪水为 40，月份 '2' 薪水为 30，月份 '1' 薪水为 20。

所以近 3 个月的薪水累计分别为 (40 + 30 + 20) = 90，(30 + 20) = 50 和 20。

| Id | Month | Salary |
| -- | ----- | ------ |
| 1  | 3     | 90     |
| 1  | 2     | 50     |
| 1  | 1     | 20     |

员工 '2' 除去最近的一个月（月份 '2'）的话，只有月份 '1' 这一个月的薪水记录。

| Id | Month | Salary |
| -- | ----- | ------ |
| 2  | 1     | 20     |

员工 '3' 除去最近一个月（月份 '4'）后有两个月，分别为：月份 '3' 薪水为 60 和 月份 '2' 薪水为 40。所以各月的累计情况如下：

| Id | Month | Salary |
| -- | ----- | ------ |
| 3  | 3     | 100    |
| 3  | 2     | 40     |

来源：力扣（LeetCode）

链接：<https://leetcode-cn.com/problems/find-cumulative-salary-of-an-employee>

著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

## Solution

```sql
SELECT Id, Month, 
    sum(Salary) over(PARTITION BY Id ORDER BY Month rows 2 preceding) Salary
FROM Employee
where (Id, Month) not in (SELECT id, max(month) from Employee GROUP BY 1)
ORDER BY 1, 2 desc;
```

## Table Schema

```sql
Create table If Not Exists Employee (Id int, Month int, Salary int);
Truncate table Employee;
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');
```


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