Question

我使用这种stackoverflow技巧已经很长一段时间了很长时间才能正常工作。 Generate an Update SQL for Changing the Order of an Item?

但如果行之间缺少记录，则无效。见这个样本，

declare @MyTable table 
(
    [ID] INT,
    [Order] INT,
    Name VARCHAR(20)
)
insert into @MyTable values(11111,1,'A'), (22222,2,'B'), (3333,3,'C'),(44444,4,'D');
select * from @MyTable;
--which will gives you
    ----------------------
--  ID    Order     Name
--  11111   1        A
--  22222   2        B
--  3333    3        C
--  44444   4        D
    ----------------------

-- Now just delete a row
delete from @MyTable where [ID] = 3333;
select * from @MyTable;
--which will gives you
    --------------------
--  ID    Order     Name
--  11111   1   A
--  22222   2   B
--  44444   4   D
    --------------------
-- Now just decrement the order of 4
declare @OldOrder INT = 4;
declare @NewOrder INT = @OldOrder - 1;

UPDATE  @MyTable 
SET [Order] = (CASE 
                WHEN 
                    [Order] = @OldOrder 
                THEN 
                    @NewOrder
                WHEN 
                    @NewOrder > @OldOrder 
                THEN 
                    [Order] - 1
                ELSE 
                    [Order] + 1 
            END)
WHERE   ([Order] BETWEEN @OldOrder AND @NewOrder OR [Order] BETWEEN @NewOrder AND @OldOrder)

select * from @MyTable;
--which will gives you
--------------------
--ID    Order   Name
--11111 1   A
--22222 2   B
--44444 3   D
--------------------

--The result should be
--------------------
--ID    Order   Name
--11111 1   A
--22222 3   B
--44444 2   D
--------------------

Answer 1

您的更新有几个问题......

UPDATE  @MyTable 
SET [Order] = (CASE 
                WHEN  [Order] = @OldOrder THEN     @NewOrder
                WHEN  @NewOrder > @OldOrder  THEN  [Order] - 1
                ELSE 
                    [Order] + 1 
            END)
WHERE   ([Order] BETWEEN @OldOrder AND @NewOrder OR [Order] BETWEEN @NewOrder AND @OldOrder)

WHEN 3 > 4 THEN [Order] - 1
WHERE ([Order] BETWEEN 4 AND 3 OR [Order] BETWEEN 3 AND 4)

您只更新此查询中的一条记录，因此输出正确。

Answer 2

你的第二个WHEN条件从未评估为真。您指定@NewOrder = @OldOrder - 1，因此@NewOrder永远不会大于@OldOrder。

改变行的顺序不起作用？

2 个答案: