如何在 MERGE 语句中限制 OUTPUT 子句的操作？

Question

这是我的查询：

MERGE INTO [payments_orders] o USING (
    SELECT 1 AS [order_id], 50.00 AS [amount] UNION ALL 
    SELECT 2 AS [order_id], 50.00 AS [amount]
) AS t ([order_id], [amount]) 
ON o.[payment_id] = 4 AND o.[order_id] = t.[order_id] 
WHEN MATCHED THEN UPDATE SET o.[amount] = t.[amount] 
WHEN NOT MATCHED THEN INSERT ([payment_id], [order_id], [amount]) 
VALUES (4, t.[order_id], t.[amount]) 
WHEN NOT MATCHED BY SOURCE AND o.[payment_id] = 4 THEN DELETE 
OUTPUT $ACTION AS [action], [deleted].[order_id];

我正在运行 MERGE 语句来插入或更新哪些订单记录与哪些付款记录相关联以及该付款的分配方式。

我想做的是在末尾添加WHERE $ACTION = 'DELETE'；然而那是行不通的。显然你不能在OUTPUT 子句中使用WHERE 子句；那是“不正确的语法”。

如何使该语句输出的唯一行是由DELETE 触发的行？

Answer 1

我遇到了同样的问题。到目前为止，我的解决方案（除非我想出另一个解决方案）是将虚拟值插入到临时表中以插入行，然后在合并语句完成后清理表。

CREATE TABLE #deleted_orders (order_id int)

MERGE INTO [payments_orders] o USING (
    SELECT 1 AS [order_id], 50.00 AS [amount] UNION ALL 
    SELECT 2 AS [order_id], 50.00 AS [amount]
) AS t ([order_id], [amount]) 
ON o.[payment_id] = 4 AND o.[order_id] = t.[order_id] 
WHEN MATCHED THEN UPDATE SET o.[amount] = t.[amount] 
WHEN NOT MATCHED THEN INSERT ([payment_id], [order_id], [amount]) 
VALUES (4, t.[order_id], t.[amount]) 
WHEN NOT MATCHED BY SOURCE AND o.[payment_id] = 4 THEN DELETE 
OUTPUT ISNULL([deleted].[order_id], -1) INTO #deleted_orders


DELETE FROM #deleted_orders WHERE order_id=-1

注意：您需要检查性能，并确定此更改是否会对您的用例造成可接受的性能影响。临时表会降低性能：请参阅“临时表”部分here for T-SQL

编辑：实际上我最终做了一些有点不同但非常相似的事情。它为您节省了最后的 DELETE 步骤

INSERT INTO #deleted_orders (order_id)
        SELECT mrg.order_id
        FROM ( MERGE INTO [payments_orders] o USING (
                    SELECT 1 AS [order_id], 50.00 AS [amount] UNION ALL 
                    SELECT 2 AS [order_id], 50.00 AS [amount]
                ) AS t ([order_id], [amount]) 
                ON o.[payment_id] = 4 AND o.[order_id] = t.[order_id] 
                WHEN MATCHED THEN UPDATE SET o.[amount] = t.[amount] 
                WHEN NOT MATCHED THEN INSERT ([payment_id], [order_id], [amount]) 
                VALUES (4, t.[order_id], t.[amount]) 
                WHEN NOT MATCHED BY SOURCE AND o.[payment_id] = 4 THEN DELETE 
                OUTPUT [deleted].[order_id] INTO #deleted_orders
OUTPUT $action as MergeAction, deleted.order_id) AS mrg 
WHERE mrg.MergeAction = 'DELETE'