[RESOLVED] Sub Query Problem

[nUflAvOrS]

SELECT SUM(SELECT (Qty * U_cost) as SubCost 
       FROM Prod_Detail 
       WHERE PCRefNo = @PCRefNo AND Product_Code = @PCode) AS TotalCost 
FROM Prod_Detail
WHERE PCRefNo = @PCRefNo AND Product_Code = @PCode

What problem of my query ?

Prompt out Incorrect Syntax near the keyword 'SELECT'