处理多个插入/更新记录时在 SQL 触发器上使用 IF UPDATE

Question

我使用此 SQL Server 触发器从特定表中查找多条记录的插入/更新，并将其放入另一个队列表（供以后处理）。

ALTER TRIGGER [dbo].[IC_ProductUpdate] ON [dbo].[StockItem]
AFTER INSERT, UPDATE
AS
BEGIN
    SELECT RowNum = ROW_NUMBER() OVER(ORDER BY ItemID) , ItemID
    INTO #ProductUpdates
    FROM INSERTED;

    DECLARE @MaxRownum INT;
    SET @MaxRownum = (SELECT MAX(RowNum) FROM #ProductUpdates);

    DECLARE @Iter INT;
    SET @Iter = (SELECT MIN(RowNum) FROM #ProductUpdates);

    WHILE @Iter <= @MaxRownum
    BEGIN
        -- Get Product Id
        DECLARE @StockItemID INT = (SELECT ItemID FROM #ProductUpdates WHERE RowNum = @Iter);

        -- Proceed If This Product Is Sync-able
        IF (dbo.IC_CanSyncProduct(@StockItemID) = 1)
        BEGIN
            -- Check If There Is A [ProductUpdate] Queue Entry Already Exist For This Product
            IF ((SELECT COUNT(*) FROM IC_ProductUpdateQueue WHERE StockItemID = @StockItemID) > 0)
            BEGIN
                -- Reset [ProductUpdate] Queue Entry
                UPDATE IC_ProductUpdateQueue 
                SET Synced = 0
                WHERE StockItemID = @StockItemID
            END
            ELSE
            BEGIN
                -- Insert [ProductUpdate] Queue Entry
                INSERT INTO IC_ProductUpdateQueue (StockItemID, Synced) 
                VALUES (@StockItemID, 0)
            END
        END

        SET @Iter = @Iter + 1;
    END

    DROP TABLE #ProductUpdates;
END

这很好用，但是我只希望上面的触发器在某些列被更新时做出反应。

我感兴趣的栏目是：

• 姓名
• 说明

我知道我可以使用以下 T-SQL 语法来检查列是否真的更新（在更新事件期间），如下所示：

IF (UPDATE(Name) OR UPDATE(Description))
BEGIN
    // do something...
END

但是，我不确定如何将其合并到上述触发器中，因为我的触发器也处理同时更新的多行。

有什么想法吗？在触发器的哪个点我可以使用IF (UPDATE(colX))？

Answer 1

首先，我建议为每个操作一个单独的触发器 - 一个用于INSERT，另一个用于UPDATE。保持代码更简洁（不那么凌乱的 IF 语句等）。

INSERT 触发器非常简单，因为无需检查更新 - 并且绝对不需要临时表和缓慢的 WHILE 循环 - 只需两个简单的基于集合的语句即可完成：

CREATE TRIGGER [dbo].[IC_ProductInsert] ON [dbo].[StockItem]
AFTER INSERT
AS
BEGIN
    -- update the queue for those entries that already exist                 
    -- those rows that *DO NOT* exist yet are not being touched
    UPDATE puq
    SET Synced = 0
    FROM dbo.IC_ProductUpdateQueue puq
    INNER JOIN Inserted i ON puq.StockItemID = i.StockItemID

    -- for those rows that don't exist yet - insert the values
    INSERT INTO dbo.IC_ProductUpdateQueue (StockItemID, Synced) 
        SELECT 
            i.StockItemID, 0
        FROM
            Inserted i
        WHERE 
            NOT EXISTS (SELECT * FROM dbo.IC_ProductUpdateQueue puq
                        WHERE puq.StockItemID = i.StockItemID)
END

UPDATE 触发器需要进行一项额外检查 - 查看感兴趣的两列之一是否已更改。这可以通过将Inserted 伪表与新值（在UPDATE 之后）和Deleted 伪表与“旧”值（在UPDATE 之前）相结合来轻松处理：

ALTER TRIGGER [dbo].[IC_ProductUpdate] ON [dbo].[StockItem]
AFTER UPDATE
AS
BEGIN
    -- update the queue for those entries that already exist                 
    -- those rows that *DO NOT* exist yet are not being touched
    UPDATE puq
    SET Synced = 0
    FROM dbo.IC_ProductUpdateQueue puq
    INNER JOIN Inserted i ON puq.StockItemID = i.StockItemID
    INNER JOIN Deleted d ON d.StockItemID = i.StockItemID
    WHERE
        i.Name <> d.Name OR i.Description <> d.Description

    -- for those rows that don't exist yet - insert the values
    INSERT INTO dbo.IC_ProductUpdateQueue (StockItemID, Synced) 
        SELECT 
            i.StockItemID, 0
        FROM
            Inserted i
        INNER JOIN 
            Deleted d ON d.StockItemID = i.StockItemID
        WHERE 
            i.Name <> d.Name OR i.Description <> d.Description
            AND NOT EXISTS (SELECT * FROM dbo.IC_ProductUpdateQueue puq
                            WHERE puq.StockItemID = i.StockItemID)
END

Answer 2

您可以加入删除并使用 where I.Name D.Name...

https://www.mssqltips.com/sqlservertip/2342/understanding-sql-server-inserted-and-deleted-tables-for-dml-triggers/