SQL Server MERGE语句和ORDER BY子句

Question

我想写一个MERGE语句,通过使用ORDER BY子句从一个大表中选择TOP 10行,并更新它的一个列值.MERGE语句允许我选择TOP 10行,但我无法将ORDER BY子句放在任何地方.

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

您可以使用表表达式作为源的表和目标MERGE.

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;

虽然使用起来可能更简单

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;