SQL Server 2000中的觸發器使用

　　示例

　　在本例中，創建了一個德國客戶表和一個墨西哥客戶表。放置在視圖上的INSTEAD OF觸發器將把更新操作重新定向到適當的基表上。這時發生的插入是對CustomersGer表的插入而不是對視圖的插入。

　　創建兩個包含客戶數據的表：

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SELECT * INTO CustomersGer FROM Customers WHERE Customers.Country = 'Germany' SELECT * INTO CustomersMex FROM Customers WHERE Customers.Country = 'Mexico' GO

　　在該數據上創建視圖：

CREATE VIEW CustomersView AS SELECT * FROM CustomersGer UNION SELECT * FROM CustomersMex GO

　　創建一個在上述視圖上的INSTEAD OF觸發器：

CREATE TRIGGER Customers_Update2 ON CustomersView INSTEAD OF UPDATE AS DECLARE @Country nvarchar(15) SET @Country = (SELECT Country FROM Inserted) IF @Country = 'Germany' BEGIN UPDATE CustomersGer SET CustomersGer.Phone = Inserted.Phone FROM CustomersGer JOIN Inserted ON CustomersGer.CustomerID = Inserted.CustomerID END ELSE IF @Country = 'Mexico' BEGIN UPDATE CustomersMex SET CustomersMex.Phone = Inserted.Phone FROM CustomersMex JOIN Inserted ON CustomersMex.CustomerID = Inserted.CustomerID END

　　通過更新視圖，測試觸發器：

UPDATE CustomersView SET Phone = ' 030-007xxxx' WHERE CustomerID = 'ALFKI' SELECT CustomerID, Phone FROM CustomersView WHERE CustomerID = 'ALFKI' SELECT CustomerID, Phone FROM CustomersGer WHERE CustomerID = 'ALFKI'

　　那么具體的講，對于多列數據，如何計算方差呢？：

CREATE TRIGGER [calT1T2T3] ON dbo.DCLB FOR INSERT,UPDATE AS update P SET /**//* 計算方差的觸發器 */ P.T1=(I.P1+I.P2+I.P3+I.P4+I.P5+I.P6), P.T2=(I.Y1+I.Y2+I.Y3+I.Y4+I.Y5+I.Y6 ), P.T3=SQRT(P.T1*P.T1+P.T2*P.T2) FROM DCLB AS P INNER JOIN Inserted AS I ON P.SID = I.SID

　　觸發器的使用很方便，而且也很簡單，重要的是理解inserted過程?？蓪PDATE語句看成兩步操作：即捕獲數據前像(before image)的DELETE語句，和捕獲數據后像(after image)的INSERT語句。當在定義有觸發器的表上執行UPDATE語句時，原始行（前像）被移入到deleted表，更新行（后像）被移入到inserted表。觸發器檢查deleted表和inserted表以及被更新的表，來確定是否更新了多行以及如何執行觸發器動作。

原文轉自：http://www.anti-gravitydesign.com