SQL问题：查询

Question

我在查询中遇到了问题。我有表product，stockRecord和priceDetail。我想展示所有产品。如果该产品的价格未在priceDetail中定义，那么它将为0.00;同样，如果数量未在stockRecord表中定义，则数量应为0.

但如果价格是在priceDetail表格中定义的，那么我们应该从表​​格中获取最新价格

WMProduct

  BusinessUnit   ProductCode    Description    SalableFlag
  MASS           0001           Pen            1
  MASS           0002           Computer       1
  MASS           0003           Book           1
  MASS           0004           Bottle         1

WMStockRecord

 ProductCode     AvailableQuantity
 0001            10
 0003            15

WMPriceDetail

 ProductCode   DateFrom      DateTo        Price
 0001          10-10-2009    10-10-2011    100
 0001          10-12-2009    10-10-2010    80
 0001          12-12-2010    01-12-2011    120
 0002          12-01-2010    ''            200
 0004          12-12-2010    12-05-2011    100

我需要这样的产品清单：

BusinessUnit  ProductCode   Description SalableFlag   Price    AvailableQuantity
MASS          0001          Pen         1             120      10
MASS          0002          Computer    1             200      0
MASS          0003          Book        1             0.00     15
MASS          0004          Bottle      1             0.00     0

Answer 1

尝试使用子查询和左连接，如下所示：

SELECT P.ProductCode AS ProductCode, 
       P.Description AS ProductName,  
       P.SalableFlag AS Salable,
       ISNULL(STK.AvailableQuantity, 0) AS Qty,
       ISNULL((SELECT TOP 1 Price FROM WMPriceDetail
               WHERE ProductCode = P.ProductCode ORDER BY DateTo DESC), 0) AS Price 
  FROM WMProduct P
  LEFT JOIN WMStockRecord STK ON P.ProductCode = STK.ProductCode