SQL Server 2008 - 如何使用DELETE觸發器更新字段

Question

我想更新記錄正在從中刪除的同一個表中的字段，但不太確定如何。該表是非常簡單，上有一個自我參考：

UserID FName EmailAddress EmailUserID 
1   Frank frank@g.com 2 
2   Jane jane@g.com NULL 
3   John john@g.com 1 
4   Brett brett@g.com 2 

這裏是我的觸發器：

CREATE TRIGGER [dbo].[CAT_DeleteUser] 
    ON Users 
    AFTER DELETE 
AS 
BEGIN 

    SET NOCOUNT ON; 

    UPDATE Users 
    SET EmailUserID = NULL 
    WHERE EmailUserID = ID_OF_DELETED_USER <-- don't know how to get this 

END 

所以，如果我刪簡（用戶ID = 2），我想觸發更新EmailUserID爲2的任何記錄。我該如何完成此操作？

Answer 1

請注意，如果您用適當的FOREIGN KEY約束設置表，後觸發器不會完成這項工作。該DELETE邏輯發生在觸發的操作之前，所以你會得到：

Msg 547, Level 16, State 0, Line 2 
The DELETE statement conflicted with the SAME TABLE REFERENCE constraint ... 

所以，如果你想要的數據完整性，使任何人都無法東西垃圾到EMailUserID列，您可以使用INSTEAD OF觸發如下：

CREATE TABLE dbo.Users 
(
    UserID INT NOT NULL PRIMARY KEY, 
    FName NVARCHAR(32), 
    EmailAddress VARCHAR(320), 
    EmailUserID INT NULL FOREIGN KEY REFERENCES dbo.Users(UserID) 
); 
GO 

CREATE TRIGGER [dbo].[CAT_DeleteUser] 
ON dbo.Users 
INSTEAD OF DELETE 
AS 
BEGIN 
    SET NOCOUNT ON; 

    -- clean up references first 
    UPDATE u SET u.EmailUserID = NULL 
     FROM dbo.Users AS u 
     INNER JOIN deleted AS d 
     ON u.EmailUserID = d.UserID; 

    -- now delete the row 
    DELETE u 
    FROM dbo.Users AS u 
    INNER JOIN deleted AS d 
    ON u.UserID = d.UserID; 
END 
GO 

樣品嚐試創建dbo.Users副本，這樣，在tempdb，然後運行這個）：

INSERT dbo.Users(UserID, FName, EmailAddress, EmailUserID) VALUES 
(1,'Frank','frank@g.com',2 ), 
(2,'Jane ','jane@g.com ',NULL), 
(3,'John ','john@g.com ',1 ), 
(4,'Brett','brett@g.com',2 ); 

SELECT * FROM dbo.Users; 
GO 

DELETE dbo.Users WHERE UserID = 2; 
GO 

SELECT * FROM dbo.Users; 
GO 

DROP TABLE dbo.Users; 
GO 

Answer 2

對不起，得到了錯誤的問題在第一時間......在這種情況下AFTER觸發器是可能的：

CREATE TRIGGER [dbo].[CAT_DeleteUser] 
    ON Users 
    AFTER DELETE 
AS 
BEGIN 

    SET NOCOUNT ON; 

    UPDATE Users 
    SET EmailUserID = NULL 
    WHERE EmailUserID IN (SELECT UserID FROM DELETED) 

END 

Answer 3

您可以使用DELETE AFTER觸發器：

CREATE TRIGGER [dbo].[CAT_DeleteUser] ON Users 
    AFTER DELETE 
AS 
BEGIN 

    SET NOCOUNT ON; 

    UPDATE Users 
    SET EmailUserID = NULL 
    FROM Users 
    JOIN DELETED 
     ON Users.EmailUserID = Deleted.UserID 

END