如何在 SQL Server 2008 的触发器中进行动态查询

Question

我当前的代码（这是错误的）

    CREATE TRIGGER [dbo].[Trg_After_Update] ON [dbo].[PurchaseDetails]
FOR UPDATE
AS
BEGIN
    UPDATE Product SET Rate = I.SallingPrice, 
        --@Result int=0;
        --if(I.Quantity > D.Quantity)
            --@Result = I.Quantity - D.Quantity
            --Stock = Stock - @Result
        --ELSE
            --@Result = D.Quantity - I.Quantity
            --Stock = Stock + @Result
    FROM Inserted I inner join deleted D on I.DetailsID = D.DetailsID
    WHERE ProductID = I.ProductID
END

当用户更新购买账单条目时，首先检查旧条目数量是否小于或大于当前数量。然后计算新旧数量之间的差异 然后使用 if 条件更新或多或少的记录和矿井和加号

Answer 1

假设我理解这个问题，你正在寻找这样的东西：

CREATE TRIGGER [dbo].[Trg_PurchaseDetails_After_Update] ON [dbo].[PurchaseDetails]
FOR UPDATE
AS
BEGIN
    UPDATE P 
    SET Rate = I.SallingPrice, 
        Stock = Stock - D.Quantity + I.Quantity
    FROM Product P
    INNER JOIN Inserted I ON P.ProductID = I.ProductID
    INNER JOIN deleted D on I.DetailsID = D.DetailsID
END

Answer 2

CREATE TRIGGER [dbo].[Trg_After_Update] ON [dbo].[PurchaseDetails]
FOR UPDATE
AS
BEGIN
    UPDATE Product SET Rate = I.SallingPrice,
    Stock = (CASE
        WHEN I.Quantity > D.Quantity
            THEN (Stock - (I.Quantity - D.Quantity))

        WHEN I.Quantity < D.Quantity
            THEN (Stock + (D.Quantity - I.Quantity))
        END)
    FROM inserted I Inner join deleted D on I.DetailsID = D.DetailsID AND I.ProductID = D.ProductID
    Where Product.ProductID = I.ProductID
END



GO

Answer 3

基于Zohar's answer 的轻微调整 - 我们的目的是根据这些购买降低库存水平，而不是提高。但是我们还需要考虑当更新处理相同ProductID 的多行时会发生什么。所以在应用更新之前我们还需要做一些聚合：

CREATE TRIGGER [dbo].[Trg_PurchaseDetails_After_Update] ON [dbo].[PurchaseDetails]
FOR UPDATE
AS
BEGIN
    UPDATE P 
    SET Rate = I.SallingPrice, 
        Stock = Stock - (I.Quantity - D.Quantity)
    FROM Product P
    INNER JOIN
        (SELECT ProductID,SUM(Quantity) as Quantity,
                MAX(SallingPrice) as SallingPrice from Inserted group by ProductID) I
             ON P.ProductID = I.ProductID
    INNER JOIN
        (SELECT ProductID,SUM(Quantity) as Quantity from deleted group by ProductID) D
             on P.ProductID = D.ProductID 
END

还请注意，我假设从每个产品的所有更新值中获取最大 SallingPrice 值是正确的。如果这不正确，我们需要一个更清晰的规范，说明对于影响具有相同 ProductID 值的多行的更新应该发生什么。

正如 Zohar 的回答下面所评论的那样，您的条件逻辑不必要地令人费解，因为 4 - (5 - 7) 和 4 + (7 - 5) 产生相同的结果，因此无需在括号内切换减法并切换外部运算符。

---

要理解我所说的聚合需求，请考虑以下脚本（使用Siddique's answer）：

create table dbo.Product (
    ProductID int not null primary key,
    Stock int not null,
    Rate int not null
)
go
insert into dbo.Product(ProductID,Stock,Rate) values (1,49,5)
go
create table dbo.PurchaseDetails (
    DetailsID int not null primary key,
    ProductID int not null,
    Quantity int not null,
    SallingPrice int not null)
go
insert into dbo.PurchaseDetails (DetailsID,ProductID,Quantity,SallingPrice) values
(1,1,10,5),
(2,1,20,10)
go
CREATE TRIGGER [dbo].[Trg_After_Update] ON [dbo].[PurchaseDetails]
FOR UPDATE
AS
BEGIN
    UPDATE Product SET Rate = I.SallingPrice,
    Stock = (CASE
        WHEN I.Quantity > D.Quantity
            THEN (Stock - (I.Quantity - D.Quantity))

        WHEN I.Quantity < D.Quantity
            THEN (Stock + (D.Quantity - I.Quantity))
        END)
    FROM inserted I Inner join deleted D on I.DetailsID = D.DetailsID AND I.ProductID = D.ProductID
    Where Product.ProductID = I.ProductID
END
go
update PurchaseDetails set Quantity = Quantity + 5
go
select * from Product
select * from PurchaseDetails

结果是：

ProductID   Stock       Rate
----------- ----------- -----------
1           44          10
DetailsID   ProductID   Quantity    SallingPrice
----------- ----------- ----------- ------------
1           1           15          5
2           1           25          10

Stock 已经调整了 5 - 但我们实际上调整了两行，并且 Stock 总数应该改变了 10，而不是 5。