MS Access SQL 查詢 - 從兩個查詢的聯合中減去數值結果

Question

我正在嘗試查詢庫存數據庫以顯示手頭剩余的蠟量。 目前這是我設置查詢的方式：

SELECT * FROM (

SELECT SUM(OC.Quantity) AS oz_Wax_Ordered
FROM Order_In AS OC 
WHERE (OC.Component) like ('Wax')
GROUP BY OC.Component

UNION SELECT SUM(C.Wax_Used) AS oz_Wax_Used
FROM Fragrance_Oils AS FO INNER JOIN Candles AS C ON FO.FragranceID = C.Fragrance
GROUP BY FO.Component
);

這向我顯示了一個列，其中第二個 SELECT 語句總計使用的蠟，第三個 SELECT 總計訂購的蠟，分別顯示在第 1 行和第 2 行。

我正在嘗試從訂購的總蠟中減去使用的總蠟。 如果需要，我可以分享有關數據庫本身的更多信息。 謝謝！

Answer 1

你可以總結這些值：

SELECT 
    SUM([oz_Wax]) AS oz_Wax_OnHand
FROM 
    (SELECT SUM(OC.Quantity) AS oz_Wax
    FROM Order_In AS OC 
    WHERE (OC.Component) like ('Wax')
    GROUP BY OC.Component

    UNION ALL
    
    SELECT -SUM(C.Wax_Used) 
    FROM Fragrance_Oils AS FO 
    INNER JOIN Candles AS C 
        ON FO.FragranceID = C.Fragrance
    GROUP BY FO.Component);