SQL Server MERGE语句和ORDER BY子句

Question

我想编写一个MERGE语句，使用ORDER BY子句从大表中选择TOP 10行，并将其更新为列值之一。 MERGE语句允许我选择TOP 10行，但无法将ORDER BY子句放在任何位置。

MERGE TOP(10) StudentAllocation AS SA 
USING (SELECT @sub_id AS subId) AS TSA ON SA.sub_id = TSA.subId 
WHEN MATCHED THEN 
     UPDATE SET SA.exam_batch = 1); 

Answer 1

您可以使用表格表达式作为MERGE的来源和目标。

WITH SA AS 
(
SELECT TOP(10) sub_id, 
       exam_batch 
FROM StudentAllocation 
ORDER BY sub_id 
) 
MERGE SA 
USING (SELECT @sub_id AS subId) AS TSA ON SA.sub_id = TSA.subId 
WHEN MATCHED THEN 
     UPDATE SET SA.exam_batch = 1; 

，虽然这可能是简单的使用

WITH SA AS 
(
SELECT TOP(10) sub_id, 
       exam_batch 
FROM StudentAllocation 
ORDER BY sub_id 
) 
UPDATE SA 
SET exam_batch = 1 
WHERE sub_id = @sub_id;