Question

我有MS SQL存储过程，它返回3个简单表中的值，如下所示，需要它在所有情况下为产品返回一行。我想知道是否可以在（T3）中获得BrandID的值，如果没有产品记录的行，则返回值为＃34; BrandID＆＃34;

T3就像

ProductID --- BrandID

@iCategoryID int
AS
Begin
SELECT P.ProductID,P.CategoryID, C.ParentID, PC.BrandID FROM T1 P
JOIN T2 C ON P.CategoryID = C.CategoryID
JOIN T3 PC ON P.ProductID=PC.ProductID
WHERE P.CategoryID=@iCategoryID 
ORDER by P.ProductID Asc
End
GO

Answer 1

您想要left outer join：

SELECT P.ProductID,P.CategoryID, C.ParentID, PC.BrandID
FROM T1 P LEFT JOIN
     T2 C
     ON P.CategoryID = C.CategoryID  LEFT JOIN
     T3 PC
     ON P.ProductID = PC.ProductID
WHERE P.CategoryID = @iCategoryID
ORDER by P.ProductID Asc;

如果品牌不匹配，则会返回NULL。如果您想改为0：

SELECT P.ProductID,P.CategoryID, C.ParentID, coalesce(PC.BrandID, 0) as BrandID
FROM T1 P LEFT JOIN
     T2 C
     ON P.CategoryID = C.CategoryID  LEFT JOIN
     T3 PC
     ON P.ProductID = PC.ProductID
WHERE P.CategoryID = @iCategoryID
ORDER by P.ProductID Asc;

MS SQL条件存储过程在所有情况下都返回值

1 个答案: