Question

我正在尝试创建一个触发器，只有在值已更改时才更新列。根据我的阅读，可以通过比较插入和删除的表来完成。以下是我尝试进行比较的方法。

还有其他方法吗？我认为select查询和if语句可以在某些方面嵌套，但我无法弄清楚如何。

CREATE TRIGGER [dbo].[tr_Persoane_Update]
   ON [dbo].[Persoane]
   AFTER UPDATE
AS BEGIN
    SET NOCOUNT ON;

    DECLARE @DFirstName varchar(30), 
            @IFirstName varchar(30), 
            @DLastName varchar(30),
            @ILastName varchar(30)

    SELECT  @DFirstName=D.FirstName, @DLastName=D.LastName
    FROM Deleted AS D
    SELECT  @IFirstName=I.FirstName, @ILastName=I.LastName
    FROM Inserted AS I

    IF @DFirstName <> @IFirstName
        BEGIN
            UPDATE FirstName
            SET  FirstName = @IFirstName
            WHERE FirstName = @DFirstName
        END
    IF @DLastName <> @ILastName 
        BEGIN
            UPDATE LastName
            SET  LastName = @ILastName
            WHERE LastName = @DLastName
        END 

END

我也试过这种方法，但我没有正确使用CASE语句。

ALTER TRIGGER [dbo].[tr_Persons_Update]
   ON [dbo].[Persons]
   AFTER UPDATE
AS BEGIN
    SET NOCOUNT ON;
    SELECT  D.FirstName, D.LastName, D.ID_Title, I.FirstName, I.LastName, I.ID_Title,
            CASE WHEN D.FirstName <> I.FirstName
                    THEN
                        BEGIN
                            UPDATE Persons
                            SET  FirstName = I.FirstName
                            WHERE FirstName = D.FirstName
                            PRINT 'FirstName modified'
                        END
            /*END                       
            CASE*/ WHEN D.LastName <> I.LastName
                    THEN
                        BEGIN
                            UPDATE Persons
                            SET  LastName = I.LastName
                            WHERE LastName = D.LastName
                            PRINT 'LastName modified'
                        END 
            /*END                       
            CASE*/ WHEN D.ID_Title <>   I.ID_Title
                    THEN
                        BEGIN
                            UPDATE Persons
                            SET ID_Title=I.ID_Title
                            WHERE ID_Title=D.ID_Title
                        END
            END
    FROM DELETED AS D
        INNER JOIN INSERTED AS I ON D.ID_Person=I.ID_Person
END

Answer 1

以下是名字的示例：

update fn
    set firstname = id.newfname
    from firstname fn join
         (select i.firstname as newfname, d.firstname as oldfname
          from inserted i join
               deleted d
               on i.personid = d.personid
          where i.firstname <> d.firstname
         ) id
         on fn.firstname = id.oldname;

您不应该假设inserted和deleted只包含一个值。这需要与{2}匹配的id inserted和deleted实际上是视图而非表格。

更新仅影响已修改列的触发器

1 个答案: