DB Engine :: How To Solve Multiple Rows Result From Inner Join Query

I have 3 tables:
 
TABLE [dbo].[Tbl_Products](
[Product_ID] [int] IDENTITY(1,1) NOT NULL,
[Product_Name] [nvarchar](50) NOT NULL,
[Catagory_ID] [int] NOT NULL,
[Entry_Date] [date] NOT NULL,

[Code] ....

I am using this query to get ( Product name from tbl_products , Buy Price - Total Price- Total Quantity from Tbl_Details )

But am getting a multiple result if the order purchase has more than 1 item :

SELECT DISTINCT B.Product_Name,A.AllPieceBoxes,
A.BuyPrice,A.TotalPrice,A.BuyPrice
FROM
Tbl_Products B INNER JOIN Tbl_PurchaseHeader C
ON C.ProductId=B.Product_ID INNER JOIN Tbl_PurchaseDetails A
ON A.PurchaseOrder=C.purchaseOrder
WHERE A.PurchaseOrder=3