滚动总和（4个月）

Question

I have been struggeling with building a query in access that calculates a "rolling 4 months" of sales data. I have been experimenting with DSUM, but I only seem to be able to get the subtotal or running total for a specific group (not a moving total). I have tried to illustrate what I am trying to do below.

    Date        Product  Value  Rolling_4_Month_Sum
    January     A        100    100
    February    A        200    300
    March       A        300    600
    April       A        300    900
    May         A        200    1000
    June        A        400    1200
    July        A        500    1400
    August      A        700    1800

Is it possible to make a running total for 4 rows/months only?

Answer 1

SELECT
 a.Date,
 a.Product,
 a.Value,
 SUM(b.value)
FROM
 Table a
 INNER JOIN Table b ON a.Product=b.Product
   AND b.Date <= a.Date
   AND b.Date >= DateAdd("q",1, a.Date)
GROUP BY
  a.Date, a.Product

This should work in my opinion.

Table a is your "single month" row date. Table b is self join to retrieve the last 4 predecessing months. It is done by adding b.Date >= DateAdd("q",1, a.Date) as self-join criteria.

Answer 2

Here is a nice example of how these kinds of things work.

Data:

OrderDetailID   OrderID ProductID   Price
1   1234    1   $5.00
2   1234    2   ($2.00)
3   1234    3   $4.00
4   1235    1   $5.00
5   1235    3   $4.00
6   1235    5   $12.00
7   1235    2   ($2.00)

SQL:

SELECT OD.OrderDetailID, OD.OrderID, OD.ProductID, OD.Price, (SELECT Sum(Price) FROM tblOrderDetails
   WHERE OrderDetailID <= OD.OrderDetailID) AS RunningSum
FROM tblOrderDetails AS OD;