[579. Find Cumulative Salary of an Employee] #leetcode

579_0902.sql

SELECT
    E1.id,
    E1.month,
    (IFNULL(E1.salary, 0) + IFNULL(E2.salary, 0) + IFNULL(E3.salary, 0)) AS Salary
FROM
    (SELECT
        id, MAX(month) AS month
    FROM
        Employee
    GROUP BY id
    HAVING COUNT(*) > 1) AS maxmonth
        LEFT JOIN
    Employee E1 ON (maxmonth.id = E1.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 id ASC , month DESC
;