我有一个相关子查询,它将返回数量列表,但我需要最高数量,而且只需要最高数量。因此,我尝试引入 order by 和 LIMIT 1 来实现此目的,但 MySQL 抛出一个错误,指出它还不支持子查询中的限制。关于如何解决这个问题有什么想法吗?
SELECT Product.Name, ProductOption.Name, a.Qty, a.Price, SheetSize.UpgradeCost,
FinishType.Name, FinishOption.Name, FinishTierPrice.Qty, FinishTierPrice.Price
FROM `Product`
JOIN `ProductOption`
ON Product.idProduct = ProductOption.Product_idProduct
JOIN `ProductOptionTier` AS a
ON a.ProductOption_idProductOption = ProductOption.idProductOption
JOIN `PaperSize`
ON PaperSize.idPaperSize = ProductOption.PaperSize_idPaperSize
JOIN `SheetSize`
ON SheetSize.PaperSize_idPaperSize = PaperSize.idPaperSize
JOIN `FinishOption`
ON FinishOption.Product_idProduct = Product.idProduct
JOIN `FinishType`
ON FinishType.idFinishType = FinishOption.Finishtype_idFinishType
JOIN `FinishTierPrice`
ON FinishTierPrice.FinishOption_idFinishOption = FinishOption.idFinishOption
WHERE Product.idProduct = 1
AND FinishTierPrice.idFinishTierPrice IN (SELECT FinishTierPrice.idFinishTierPrice
FROM `FinishTierPrice`
WHERE FinishTierPrice.Qty <= a.Qty
ORDER BY a.Qty DESC
LIMIT 1)
这是一个变体greatest-n-per-group
经常出现的问题。
您需要单行形式 FinishTierPrice (将其称为p1
),匹配 FinishOption 并具有最大数量,但仍小于或等于 ProductOptionTier 的数量。
一种方法是尝试匹配第二行(p2
)来自 FinishTierPrice,它将具有相同的 FinishOption 和更大的数量。如果不存在这样的行(使用外连接并测试它是否为 NULL),则通过p1
是最伟大的。
SELECT Product.Name, ProductOption.Name, a.Qty, a.Price, SheetSize.UpgradeCost,
FinishType.Name, FinishOption.Name, FinishTierPrice.Qty, FinishTierPrice.Price
FROM `Product`
JOIN `ProductOption`
ON Product.idProduct = ProductOption.Product_idProduct
JOIN `ProductOptionTier` AS a
ON a.ProductOption_idProductOption = ProductOption.idProductOption
JOIN `PaperSize`
ON PaperSize.idPaperSize = ProductOption.PaperSize_idPaperSize
JOIN `SheetSize`
ON SheetSize.PaperSize_idPaperSize = PaperSize.idPaperSize
JOIN `FinishOption`
ON FinishOption.Product_idProduct = Product.idProduct
JOIN `FinishType`
ON FinishType.idFinishType = FinishOption.Finishtype_idFinishType
JOIN `FinishTierPrice` AS p1
ON p1.FinishOption_idFinishOption = FinishOption.idFinishOption
AND p1.Qty <= a.Qty
LEFT OUTER JOIN `FinishTierPrice` AS p2
ON p2.FinishOption_idFinishOption = FinishOption.idFinishOption
AND p2.Qty <= a.Qty AND (p2.Qty > p1.Qty OR p2.Qty = p1.Qty
AND p2.idFinishTierPrice > p1.idFinishTierPrice)
WHERE Product.idProduct = 1
AND p2.idFinishTierPrice IS NULL
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