如何在没有主键的情况下合并UPDATE中的2行或多行并求和一列?

每个表都应该有一个主键。在这种情况下,主键应该是 CTransaction, CItemCode, CUOM 并且您应该修复这个过程来打乱这一正在进行的操作,而不是添加新的重复行。

可以使用 MERGE 尽管如此。一种方法如下(为每组更新任意一个,并删除其余部分)。

WITH Tgt AS
(
SELECT *, 
        SumCQuantity = SUM(CQuantity) OVER (PARTITION BY CTransaction, CItemCode, CUOM ),
        rn = ROW_NUMBER() OVER (PARTITION BY CTransaction, CItemCode, CUOM  ORDER BY CTransaction) 
FROM YourTable
) 
Merge Tgt with (HOLDLOCK)
USING (VALUES(1)) src(rn) ON Tgt.rn = 1
WHEN MATCHED AND CQuantity IS DISTINCT FROM SumCQuantity THEN 
    UPDATE SET CQuantity = SumCQuantity 
WHEN NOT MATCHED BY SOURCE THEN 
    DELETE;

Fiddle

考虑到您已经说过可能需要定期进行此汇总,使用您已经创建的聚合查询在源表的顶部创建一个视图可能是最有意义的:

CREATE VIEW yourView AS
SELECT CTransaction, CItemCode, CUOM, SUM(CQuantity)
FROM yourTable
GROUP BY CTransaction, CItemCode, CUOM;

那就用 SELECT * FROM yourView 只要您需要访问这些数据。