如何使動態查詢在Triiger在SQL Server 2008

Question

我當前的代碼（這是錯誤的）

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 

當用戶更新採購紙幣入口，那麼首先Cheack無論舊條目數量比目前的數量小於或大於。再算上新老產品數量 然後更新記錄在或大或小批量，礦業和另外使用。如果條件

Answer 1

假設我明白的問題之間Diffrence，您正在尋找這樣的事情：

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

輕微根據Zohar's answer進行調整 - 我們打算根據這些購買量降低庫存水平，而不是增加。但是我們也需要考慮在處理相同的ProductID的多行更新時會發生什麼情況。因此，我們需要在應用更新前做一些彙總，以及：

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 

還請注意，我認爲這是正確的，從每一個產品的所有更新的值取最大值SallingPrice值。如果這是不正確的，我們需要更清楚地說明對於影響具有相同ProductID值的多行的更新應該發生的情況。

正如下面評論佐哈爾的答案，你的條件邏輯是不必要的令人費解，因爲4 - (5 - 7)和4 + (7 - 5)產生相同的結果，沒有必要切換周圍的括號內的減法和切換外操作。

---

要明白我與需要聚集談論，考慮下面的腳本（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 

結果是：

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

股票已經調整了5 - 但我們實際調整了兩排，總庫存應該已經改變了10，而不是5.

Answer 3

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