Question

我需要监控表上的字段子集，并在其中一个字段发生更改时执行任务。

我在表更新时使用触发器，然后查看更改，如下所示：

-- join the deleted and inserted to get a full list of rows
select * into #tmp from (select * from inserted union select * from deleted) un
-- select a count of differing rows, > 1 means something is different
select distinct count(*) from #tmp

这很好，计数为2或更多意味着单行更新有所不同。问题是，如果我正在进行多行更新，那么这会破坏。

我有没有办法让这个可以用于多行更新，或者我是否需要完全尝试不同的方法。

Answer 1

你可以这样做（语法完全未经测试）

IF NOT UPDATE(col) 
 RETURN

SELECT inserted.key, inserted.col as i_col,  deleted.col as d_col
INTO #interestingrows
 FROM inserted JOIN deleted on inserted.key = deleted.key 
    and inserted.col <> deleted.col /*If col is nullable cater for that as well*/

IF @@ROWCOUNT=0
 RETURN

 /*Process contents of  #interestingrows*/

Answer 2

我最终找到了一个相当简单的解决方案。我在检查中写了一个额外的循环，它在插入的每行检查。

        -- get a list of updated line id's
        select field1 as id into #loop from inserted 



    -- loop through all the id's and do a compare
    while (select count(*) from #loop) > 0 begin
        select top 1 @id = id from #loop

        select * into #tmp from (select * from inserted where field1 = @id union 
                                 select * from deleted where field1 = @id) un

        -- do a select ditinct to count the differing lines.
        if (select distinct count(*) from #tmp) > 1 begin
            -- the 2 lines don't match, so mark for update
            update test1 set flag = 1 where field1 = @id
        end
        drop table #tmp

        delete #loop where id = @id
    end

检查触发器中是否有变化

2 个答案: