SQL Server 2008-如何使用删除触发器更新字段
我想更新同一个表中的一个字段,该表中的记录正在被删除,但不太确定如何更新。该表非常简单,上面有一个自引用:SQL Server 2008-如何使用删除触发器更新字段,sql,sql-server-2008,Sql,Sql Server 2008,我想更新同一个表中的一个字段,该表中的记录正在被删除,但不太确定如何更新。该表非常简单,上面有一个自引用: 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 这是我的扳机: CREA
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
这是我的扳机:
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janeuserid=2,我希望触发器用EmailUserID为2更新任何记录。我怎样才能做到这一点 对不起,第一次问错了问题。。。在这种情况下,后触发是可能的:
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
您可以使用删除后触发器:
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
请注意,如果使用适当的外键约束设置表,after触发器将不会执行此任务。删除逻辑上发生在触发器中的操作之前,因此您将得到:
Msg 547, Level 16, State 0, Line 2
The DELETE statement conflicted with the SAME TABLE REFERENCE constraint ...
因此,如果您确实希望数据完整性,这样就没有人可以将垃圾塞进EMailUserID列中,那么您可以使用一个INSTEAD OF触发器,如下所示:
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tempdb中创建dbo.Users的副本,如上所述,然后运行以下操作:
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
你能简单解释一下吗?从外观上看,这将更新UserID为DELETE UserID的用户表,除非您想将where EmailUserID放入SELECT UserID FROM DELETED中。@Robert:如果行受原始DELETE语句影响,您想更新用户表并将列EmailUserID设置为null,对吗?假设UserID是表的主键,触发器将所有行中的EmailUserID设置为null,这些行是由原始的delete语句删除的。您正在更新用户标识匹配的行。我同意@Oleg,你需要更仔细地研究这个问题。我已经做了两个更正。没有ID列;更正为UserID。还限定了加入,因为EmailUserID同时存在于用户和已删除用户中-由于列名称不明确,这应该无法解析。您知道,只有在没有自引用外键的情况下,这才有效,对吗?这意味着您可以在EmailUserID中填充任何值,SQL Server不会抱怨。