mysql 累加求和

有如下表
id money
1 10
2 20
3 30
4 40

求出如下数据
id money cum
1 10 10
2 20 30
3 30 60
4 40 100

建表
CREATE TABLE cum_demo
(id INT,money INT,PRIMARY KEY (id))

插入数据
insert into cum_demo(id,money)
values (1,10),(2,20),(3,30),(4.40);

求累加
SELECT a.id,a.money,SUM(lt.money) as cum
FROM cum_demo a JOIN cum_demo lt
ON a.id >= lt.id
GROUP BY a.money
ORDER BY id

结果
id money cum
1 10 10
2 20 30
3 30 60
4 40 100