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如果条件LEFT JOIN为false,如何让它为空而不是跳过它? 这部分代码:如果条件LEFT JOIN为false,如何让它为空而不是跳过它?
SELECT
c.Name,
p.Name
FROM Category c
LEFT JOIN ProductCategory pc ON c.CategoryID = pc.CategoryID
LEFT JOIN Product p ON pc.ProductID = p.ProductID
WHERE pc.ProductID = 17;
结果必然是:
FirstCategory SeventeenProduct
SecondCategory SeventeenProduct
ThirdCategory null
FourthCategory SeventeenProduct
等等