Question

我在“订单”表中添加了“FirstDesignTitle”列，并尝试更新其初始值（然后通过业务逻辑使其保持最新）。我的表是：

Orders
------
OrderID
FirstDesignTitle


LineItem
--------
LineItemID
OrderID
DesignID


Design
------
DesignID
DesignTitle

“First”表示具有DesignID的最低LineItemID'd LineItem（该列可以为空）。我得到的更新声明是：

UPDATE Orders
SET FirstDesignTitle = t.DesignTitle
FROM (
    SELECT TOP (1) [t4].[value] as DesignTitle
    FROM (
        SELECT (
            SELECT [t3].[DesignTitle]
            FROM (
                SELECT TOP (1) [t1].[DesignID]
                FROM [dbo].[LineItem] AS [t1]
                WHERE ([t1].[DesignID] IS NOT NULL) AND ([t1].[OrderID] = [t0].[OrderID])
                ORDER BY [t1].[LineItemID] ASC
                ) AS [t2]
            LEFT OUTER JOIN [dbo].[Design] AS [t3] ON [t3].[DesignID] = [t2].[DesignID]
        ) AS [value], [t0].[OrderID]
        FROM [dbo].[Orders] AS [t0]
    ) AS [t4]
    WHERE [t4].[OrderID] = orderid
    ORDER BY DesignTitle DESC
) t

但是，我只得到一个DesignTitle来填充所有订单，而不是我想要的，这是每个订单显示其第一个LineItem的DesignTitle。填充的DesignTitle是Designs表中最后一个DesignTitle，以字母“ZZZ”开头。谁能描述/修复我做错了什么？

Answer 1

这是使用CTE实现目标的方法

;WITH CTELineItem
AS
(
    SELECT Sequence = ROW_NUMBER() OVER(PARTITION BY OrderID ORDER BY LineItemID ASC),
            OrderID,
            DesignID
    FROM LineItem
    WHERE DesignID IS NOT NULL
)

UPDATE Orders
SET Orders.FirstDesignTitle = Design.DesignTitle
FROM Orders
INNER JOIN CTELineItem AS FirstLineItem ON FirstLineItem.Sequence = 1 
                                        AND Orders.OrderID = FirstLineItem.OrderID
INNER JOIN Design ON FirstLineItem.DesignID = Design.DesignID

Answer 2

我不知道为什么你的查询不起作用。另一种方法使用相关子查询：

update orders
    set firstdesigntitle = (select top 1 d.designtitle
                            from lineitem li join
                                 design d
                                 on li.designid = d.designid
                            where li.orderid = orders.orderid
                            order by d.designid asc
                           );

您没有指定如何定义“first”。这使用最小的designid。

这个SQL更新语句有什么问题

2 个答案: