当我在 tsql 上更新一条记录的 OrderNo 时如何更新其他 OrderNo

Question

我有一个名为“问题”的问题表，它的 OrderNo 定义了问题的顺序。

我在更新 OrderNo 时遇到了问题。

如果我更新了其中一个 OrderNo，则必须更新所有 OrderNo 取决于更新后的 OrderNo，因此所有订单都会更新。

解决方案之一是光标，但我没有解决这个问题。

你有什么建议吗？

Answer 1

以下代码演示了一种以给定的显示顺序重新定位行的方法，并打乱任何其他行以适应更改。通过使用case 表达式，单个update 语句可以选择如何更新不同的行。

注意：它应该被包装在一个合适的交易中，以便在 The Real Word 中使用。

-- Sample data.
declare @Samples as Table ( Id Int Identity, DisplayOrder Int );
insert into @Samples ( DisplayOrder ) values ( 1 ), ( 2 ), ( 3 ), ( 4 );
select * from @Samples order by DisplayOrder;

-- We need a few variables.
declare @PreviousDisplayOrder as Int;
declare @Id as Int, -- Row to be moved.
  @DisplayOrder as Int; -- New order for the row.

-- Pick a row to move and a new display order for it.
select @Id = 2, @DisplayOrder = 3;

-- Determine the previous display order for the row being moved.
select @PreviousDisplayOrder = DisplayOrder from @Samples where Id = @Id;

-- Display some useful tidbits.
select @PreviousDisplayOrder as PreviousDisplayOrder,
  ( select Min( DisplayOrder ) from ( values ( @DisplayOrder ), (@PreviousDisplayOrder ) ) M1( DisplayOrder ) ) as MinDisplayOrder,
  ( select Max( DisplayOrder ) from ( values ( @DisplayOrder ), (@PreviousDisplayOrder ) ) M2( DisplayOrder ) ) as MaxDisplayOrder;

-- Update the rows.
update @Samples
  set DisplayOrder = case
    -- Set the order of the repositioned row.
    when Id = @Id then @DisplayOrder
    -- Moving the repositioned row up (numerically).
    when @DisplayOrder > @PreviousDisplayOrder and DisplayOrder <= @DisplayOrder then DisplayOrder - 1
    -- Moving the repositioned row down (numerically).
    when @DisplayOrder < @PreviousDisplayOrder and DisplayOrder >= @DisplayOrder then DisplayOrder + 1
    else DisplayOrder
    end
    where
      -- Only update the rows between the original and the new display orders.
      DisplayOrder >= ( select Min( DisplayOrder ) from ( values ( @DisplayOrder ), (@PreviousDisplayOrder ) ) M1( DisplayOrder ) ) and
      DisplayOrder <= ( select Max( DisplayOrder ) from ( values ( @DisplayOrder ), (@PreviousDisplayOrder ) ) M2( DisplayOrder ) );

-- Display the results.
select * from @Samples order by DisplayOrder;