SQL Server更新触发器，仅获取修改后的字段 [英] SQL Server Update Trigger, Get Only modified fields

问题描述

我知道 COLUMNS_UPDATED ，所以我需要一些快速捷径（如果有人制造了，我已经制造了，但是如果有人可以节省我的时间，我会

I am aware of COLUMNS_UPDATED, well I need some quick shortcut (if anyone has made, I am already making one, but if anyone can save my time, I will appriciate it)

我基本上需要仅具有更新的列值的XML，出于复制目的，我需要它。

I need basicaly an XML of only updated column values, I need this for replication purpose.

SELECT * FROM插入为我提供了每一列，但我只需要更新列。

SELECT * FROM inserted gives me each column, but I need only updated ones.

类似于以下内容...

something like following...

CREATE TRIGGER DBCustomers_Insert
    ON DBCustomers
    AFTER UPDATE
AS
BEGIN
    DECLARE @sql as NVARCHAR(1024);
    SET @sql = 'SELECT ';


    I NEED HELP FOR FOLLOWING LINE ...., I can manually write every column, but I need 
    an automated routin which can work regardless of column specification
    for each column, if its modified append $sql = ',' + columnname...

    SET @sql = $sql + ' FROM inserted FOR XML RAW';

    DECLARE @x as XML;
    SET @x = CAST(EXEC(@sql) AS XML);


    .. use @x

END

推荐答案

在触发器内，您可以像这样使用 COLUMNS_UPDATED（）来获取更新的值

Inside the trigger, you can use COLUMNS_UPDATED() like this in order to get updated value

-- Get the table id of the trigger
--
DECLARE @idTable      INT

SELECT  @idTable = T.id 
FROM    sysobjects P JOIN sysobjects T ON P.parent_obj = T.id 
WHERE   P.id = @@procid

-- Get COLUMNS_UPDATED if update
--
DECLARE @Columns_Updated VARCHAR(50)

SELECT  @Columns_Updated = ISNULL(@Columns_Updated + ', ', '') + name 
FROM    syscolumns 
WHERE   id = @idTable   
AND     CONVERT(VARBINARY,REVERSE(COLUMNS_UPDATED())) & POWER(CONVERT(BIGINT, 2), colorder - 1) > 0

但是当您的表中有62列以上时，此代码段将失败。溢出...

But this snipet of code fails when you have a table with more than 62 columns.. Arth.Overflow...

这里是最终版本，可处理62列以上，但仅提供更新的列数。很容易与 syscolumns链接以获得名称

Here is the final version which handles more than 62 columns but give only the number of the updated columns. It's easy to link with 'syscolumns' to get the name

DECLARE @Columns_Updated VARCHAR(100)
SET     @Columns_Updated = ''   

DECLARE @maxByteCU INT
DECLARE @curByteCU INT
SELECT  @maxByteCU = DATALENGTH(COLUMNS_UPDATED()), 
        @curByteCU = 1

WHILE @curByteCU <= @maxByteCU BEGIN
    DECLARE @cByte INT
    SET     @cByte = SUBSTRING(COLUMNS_UPDATED(), @curByteCU, 1)

    DECLARE @curBit INT
    DECLARE @maxBit INT
    SELECT  @curBit = 1, 
            @maxBit = 8
    WHILE @curBit <= @maxBit BEGIN
        IF CONVERT(BIT, @cByte & POWER(2,@curBit - 1)) <> 0 
            SET @Columns_Updated = @Columns_Updated + '[' + CONVERT(VARCHAR, 8 * (@curByteCU - 1) + @curBit) + ']'
        SET @curBit = @curBit + 1
    END
    SET @curByteCU = @curByteCU + 1
END

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