。減去2別名列

Question

我通過兩個查詢到inn和out別名列，我想這樣做， res=(inn-out)，但它給我一個錯誤

Invalid column name 'inn'. 
Invalid column name 'out'. 
? 

select productname 
,inn=isnull((select sum(orderqty) 
       from purchasing.purchaseinvoicedetail 
       where productfk=Production.product.productid),0) 
,outt=isnull((select sum(orderqty) 
       from sales.salesinvoicedetail 
       where productfk=Production.product.productid ),0) 
,res=(inn-outt) 
from production.product 

Answer 1

試試這個inn和outt只能在外面引用

Select a.*,inn-outt As [DiffValue] from 
    (
    select productname,inn=isnull((select sum(orderqty) from purchasing.purchaseinvoicedetail where productfk=Production.product.productid),0), 
     outt=isnull((select sum(orderqty) from sales.salesinvoicedetail where productfk=Production.product.productid ),0) 
     from production.product 

     ) As a 

Answer 2

試試這個：

SELECT t.*, t.Inn - t.outt AS Res 
FROM 
(
select productname 
,inn=isnull((select sum(orderqty) 
       from purchasing.purchaseinvoicedetail 
       where productfk=Production.product.productid),0) 
,outt=isnull((select sum(orderqty) 
       from sales.salesinvoicedetail 
       where productfk=Production.product.productid ),0) 
from production.product 
) t