The Employee table holds the salary information in a year.
Write a SQL to get the cumulative sum of an employee's salary over a period of 3 months but exclude the most recent month.
The result should be displayed by 'Id' ascending, and then by 'Month' descending.
Example
Input
| 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 |
Output
| Id | Month | Salary | |----|-------|--------| | 1 | 3 | 90 | | 1 | 2 | 50 | | 1 | 1 | 20 | | 2 | 1 | 20 | | 3 | 3 | 100 | | 3 | 2 | 40 |
Explanation
Employee '1' has 3 salary records for the following 3 months except the most recent month '4': salary 40 for month '3', 30 for month '2' and 20 for month '1'
So the cumulative sum of salary of this employee over 3 months is 90(40+30+20), 50(30+20) and 20 respectively.
| Id | Month | Salary | |----|-------|--------| | 1 | 3 | 90 | | 1 | 2 | 50 | | 1 | 1 | 20 |
Employee '2' only has one salary record (month '1') except its most recent month '2'.
| Id | Month | Salary | |----|-------|--------| | 2 | 1 | 20 |
Employ '3' has two salary records except its most recent pay month '4': month '3' with 60 and month '2' with 40. So the cumulative salary is as following.
| Id | Month | Salary | |----|-------|--------| | 3 | 3 | 100 | | 3 | 2 | 40 |