SUM based on date range in query builder

[tjstromquist]

I would like to create some custom columns of data within my query.

I would like to create the following column: Last4WeeksQty. It would be something like
Last4WksQty: IIf(([dbo_Depot_Buckets.Date_Start]) Between (([dbo_Depot_Buckets.Date_Start])-21) And ([dbo_Depot_Buckets.Date_Start]),([Qty_Sold]),0))

The above formula retuns a number but it is not summing correctly, it is just returning the qty of that week....

Current query shows:

Year	DateStart	Week	SKU	Qty	Dlrs
2012	03-26-2012	9	315554	10	45
2012	03-19-2012	8	55456	15	66
2012	03-12-2012	7	654496	154	545
2012	03-05-2012	6	465465	654	654
2012	02-27-2012	5	56684	544	441

[jzwp11]

You would need to use either a subquery or a DSum() function to accomplish what you are after