SQL Server 2008 dbms and Visual Studio

I need to add one more column in gridview as difference of Supplier_Quantity - Store_quantity and that difference should store in new column after the supplier_Quantity when I click on Calculate button column what should I do?

I try the following query

select 
    Product_Name, Supplier_Quantity, Store_Quantity,
    'DIFFRENCE' = Supplier_Quantity - Store_Quantity 
from 
    relatesupp

but it shows in sql only and as soon as I use it in Visual Studio it doesn't show in gridview.