使用分组累积先前的行

Question

我在MS SQL Server上有这个表

Customer    Month    Amount
-----------------------------
Tom         1        10
Kate        1        60
Ali         1        70
Tom         2        50
Kate        2        40
Tom         3        80
Ali         3        20

我希望select能够每个月积累客户

Customer    Month    Amount
-----------------------------
Tom         1        10
Kate        1        60
Ali         1        70
Tom         2        60
Kate        2        100
Ali         2        70
Tom         3        140
Kate        3        100
Ali         3        90

注意到Ali没有2个月的数据,Kate没有3个月的数据

我已经做到了,但问题是,对于每个客户的缺失月份没有数据显示,Kate必须在第3个月有100个金额,而Ali必须在第2个月有70个金额

declare @myTable as TABLE   (Customer varchar(50), Month int, Amount int)
;

INSERT INTO @myTable
    (Customer, Month, Amount)
VALUES
    ('Tom', 1, 10),
    ('Kate', 1, 60),
    ('Ali', 1, 70),
    ('Tom', 2, 50),
    ('Kate', 2, 40),
    ('Tom', 3, 80),
    ('Ali', 3, 20);


select * from @myTable


select
    SUM(b.Amount),a.Customer, a.Month
from
    @myTable a
        inner join
    @myTable b
        on a.Customer = b.Customer and 
            a.Month >= b.Month
group by
    a.Customer, a.Month

Answer 1

明确（在回答金额和金额总和中）

DECLARE @myTable TABLE(Customer varchar(50), Month int, Amount int);

INSERT INTO @myTable(Customer, Month, Amount)
VALUES
    ('Tom', 1, 10),
    ('Kate', 1, 60),
    ('Ali', 1, 70),
    ('Tom', 2, 50),
    ('Kate', 2, 40),
    ('Tom', 3, 80),
    ('Ali', 3, 20);


DECLARE @FullTable TABLE(Customer varchar(50), Month int, Amount int);

INSERT INTO @FullTable(Customer, Month, Amount)
SELECT c.Customer, m.Month, ISNULL(mt.Amount, 0)
FROM (SELECT DISTINCT [Month] FROM @myTable) AS m
CROSS JOIN (SELECT DISTINCT Customer FROM @myTable) AS c
LEFT JOIN @myTable AS mt ON m.Month = mt.Month AND c.Customer = mt.Customer


SELECT t1.Customer, t1.Month, t1.Amount, (t1.Amount + ISNULL(t2.sm, 0)) AS AmountSum
FROM @FullTable AS t1
CROSS APPLY (SELECT SUM(Amount) AS sm FROM @FullTable AS t WHERE t.Customer = t1.Customer AND t.Month < t1.Month) AS t2
ORDER BY Month, Customer