访问SQL查询内部联接并以null求和

Question

表格：项目，采购，报价行。

项目具有字段ItemID，ItemName，IsActive
购买具有字段ItemID，QtyPurchased
QuoteLines具有字段ItemID，NegQty，IsSold

目标是选择IsActive = yes的所有ItemID，然后对所有QtyPurchased求和，并仅减去IsSold = yes的NeqQty。

我努力了：

SELECT Items.ItemID, Items.ItemName, IIF(NegQTY=NULL, SUM(QtyPurchased), SUM(NegQty+PurchasedQty)) AS Inv_Qty
FROM Purchases, Items, QuoteLines
WHERE Purchases.ItemID=Items.ItemID AND Items.ItemID=QuoteLines.ItemID
GROUP BY Items.ItemID, Items.ItemName;

结果导致“您的查询不包含指定的表达式IIF（NegQTY = NULL，SUM（QtyPurchased），SUM（NegQty + PurchasedQty））”

我还尝试了tblItems和tblPurchases之间的内部联接以获取PurchasedQty，然后在tblItems和tblQuoteLines之间进行第二次内部联接以仅获取SoldQty，然后在PurchasedQty和SoldQty之间进行左内部联接以获取InventoryQty，但这为在PurchasedQty和SoldQty中都存在的项目，但是对于仅在PurchasedQty中存在的项目，它返回NULL。

Answer 1

考虑使用保存的查询来计算购买的总单位和销售的总单位，然后在查询中使用那些保存的查询来计算当前库存。

购买的总单位

创建一个名为[TotalPurchasedByItemID]的保存的查询

SELECT 
    Items.ItemID, 
    Sum(Purchases.QtyPurchased) AS SumOfQtyPurchased
FROM 
    Items 
    INNER JOIN 
    Purchases 
        ON Items.ItemID = Purchases.ItemID
WHERE (((Items.IsActive)=True))
GROUP BY Items.ItemID;

售出总单位

创建一个名为[TotalSoldByItemID]的保存的查询

SELECT 
    Items.ItemID, 
    Sum(QuoteLines.NegQty) AS SumOfNegQty
FROM 
    Items 
    INNER JOIN 
    QuoteLines 
        ON Items.ItemID = QuoteLines.ItemID
WHERE (((Items.IsActive)=True) AND ((QuoteLines.IsSold)=True))
GROUP BY Items.ItemID;

当前库存

SELECT 
    Items.ItemID, 
    Items.ItemName, 
    Nz([SumOfQtyPurchased],0)-Nz([SumOfNegQty],0) AS Inv_Qty
FROM 
    (
        Items 
        LEFT JOIN 
        TotalPurchasedByItemID 
            ON Items.ItemID = TotalPurchasedByItemID.ItemID
    ) 
    LEFT JOIN 
    TotalSoldByItemID 
        ON Items.ItemID = TotalSoldByItemID.ItemID
WHERE (((Items.IsActive)=True));