SQL Server 2008 - 如何使用DELETE触发器更新字段

Question

我想更新记录被删除的同一个表中的字段,但不太确定如何.该表非常简单,并有自我参考:

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

这是我的触发器:

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

因此,如果我删除Jane(UserID = 2),我希望触发器更新任何记录,其EmailUserID为2.如何实现此目的？

Answer 1

您可以使用AFTER DELETE Trigger:

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

Answer 2

请注意，如果使用适当的FOREIGN KEY约束来设置表，则after触发器将无法完成工作。从DELETE逻辑上讲，这发生在触发器中的操作之前，因此您将获得：

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

因此，如果您确实想要数据完整性，以便没有人可以将垃圾填入EMailUserID列，则可以使用INSTEAD OF如下所示的触发器：

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

示例尝试在中创建的副本dbo.Users，如上所示tempdb，然后运行以下命令）：

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