MS Access SQL 查询 - 从两个查询的联合中减去数值结果

Question

我正在尝试查询库存数据库以显示手头剩余的蜡量。 目前这是我设置查询的方式：

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
);

这向我显示了一个列，其中第二个 SELECT 语句总计使用的蜡，第三个 SELECT 总计订购的蜡，分别显示在第 1 行和第 2 行。

我正在尝试从订购的总蜡中减去使用的总蜡。 如果需要，我可以分享有关数据库本身的更多信息。 谢谢！

Answer 1

你可以总结这些值：

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);