DSum Function To Sum Sales Of Each Customer?

Can Dsum function sums the sales of each customer. For example, let say we have the following query

Code:
QueryCustomerSales
Customer Name
Order ID
Item
Amount
Price

So, can i get output something like :

Code:
John 200.540 $
Mark 300.350 $

I tried the following code "

Code:
Dsum ("[Amount] * [Price]", "QueryCustomerSales", "[Customer Name]= [Customer Name]")

However, it returns the sales of all customers (all together ):

Code:
John 500.890 $
Mark 500.890 $