LeetCode--579. 查询员工的累计薪水

建表

DROP TABLE IF EXISTS employee;
CREATE TABLE employee
(
Id INT,
MONTH INT,
Salary DECIMAL
);
INSERT INTO employee VALUES(1, 1, 20);
INSERT INTO employee VALUES(2, 1, 20);
INSERT INTO employee VALUES(1, 2, 30);
INSERT INTO employee VALUES(2, 2, 30);
INSERT INTO employee VALUES(3, 2, 40);
INSERT INTO employee VALUES(1, 3, 40);
INSERT INTO employee VALUES(3, 3, 60);
INSERT INTO employee VALUES(1, 4, 60);
INSERT INTO employee VALUES(3, 4, 70);
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解题思路

用开窗函数求薪水，对id分组然后根据月份降序排列，需要去掉最近一个月即去掉top1

注意题目要求是三个月的总额,所以要加 ROWS 2 PRECEDING，将当前行和它前面的两行划为一个窗口

SELECT t.id, t.`month`, t.salary FROM
(
 SELECT id, `month`, 
 SUM(salary) over(PARTITION BY id ORDER BY `month` ROWS 2 PRECEDING) salary, -- 累加的总薪水
 rank() over(PARTITION BY id ORDER BY `month` DESC) ranks   -- 排名好去掉最近一个月
 FROM employee
) t
WHERE t.ranks > 1
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