sql - 创建触发器以将列值插入到同一表的其他列 SQL Server 2005

Question

如何创建触发器以在表中新插入行的同一表的另一列的值相同的列中插入值。

假设我有如下表

ColumnA | ColumnB

我希望在将行插入表中或更新ColumnB值后立即将ColumnB值插入到ColumnA中。但反之亦然，即将columnA 值插入columnB

.下面的代码仅处理插入，请帮助我如何处理表的插入和更新，即当插入或更新columnB值时。

CREATE TRIGGER inserupdate
   ON  triggertestTable
   AFTER INSERT,UPDATE
AS 
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    -- Insert statements for trigger here
    declare @value int

    select @value=columnB from inserted

    update triggertestTable
    set columnA=@value

END
GO

如果像下面这样插入值，则效果很好

insert into triggertestTable(columnB) values('xyz')

ColumnB 值被插入到 columnA

ColumnA | ColumnB
  xyz   |  xyz 

但是，如果其他应用程序在列 A 中插入值，则空值会在两者中更新

 insert into triggertestTable(columnA) values('pqr')

现在记录是

ColumnA | ColumnB
  xyz   |  xyz 
  NULL  |  NULL

正确的记录集应该如下所示

  ColumnA   | ColumnB
      xyz   |  xyz 
      pqr   |  NULL

如何解决这个问题。

Answer 1

尝试此触发器(当将值插入 ColumnB 或更新 ColumbB 中的值时，它将把值从 ColumnB 复制到 ColumnA):

CREATE TRIGGER trgIU_triggertestTable_UpdateColumnAWhenColumnB
   ON  dbo.triggertestTable
   AFTER INSERT,UPDATE
AS 
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

    IF UPDATE(ColumnB)
    BEGIN
        UPDATE  dbo.triggertestTable
        SET     ColumnA=i.ColumnB
        FROM    inserted i
        INNER JOIN dbo.triggertestTable t ON i.MyID=t.MyID
        LEFT JOIN deleted d ON i.MyID=d.MyID
        WHERE   d.MyID IS NULL AND i.ColumnB IS NOT NULL -- Row was inserted
        OR      d.MyID IS NOT NULL -- Row was updated
    END
END
GO

我使用了这张表:

CREATE TABLE dbo.triggertestTable(
    MyID INT IDENTITY(1,1) PRIMARY KEY, -- MyID should be a PRIMARY KEY or a mandatory(NOT NULL) UNIQUE constraint
    ColumnA VARCHAR(100),
    ColumnB VARCHAR(100)
);
GO