SQL Running Subtraction

Question

I have a result set as below:

Item    ExpectedQty  ReceivedQty  Short
Item01  30           45           5
Item01  20           45           5

Item02  40             


        

Answer 1

SELECT  a.ExpectedQty,
    b.ReceivedQty,
    CASE WHEN b.ReceivedQty < a.ExpectedQty
         THEN b.ReceivedQty - a.ExpectedQty
         ELSE 0
    END Short
FROM    dbo.a a
INNER JOIN dbo.b b
ON      a.ItemId = b.ItemId