从上面的值填充列值，直到它在SQL Server中达到新值

Posted 2021-05-03

目前，我有一个表格，其值填写如下：

我需要添加一个触发器来填充insert上的值，因此最终结果如下所示：

在excel中的过程类似于您向下拖动值。但我需要它在它达到新值之前停止，然后重新开始这个过程。

但是，有时可能没有下一个值。如果没有结束，我将如何停止更新？

答案

您可以使用两个相关的子查询来完成此操作。

create table #YourTable (RowNumber int identity(1,1), [Value] int null)
insert into #YourTable 
values
(10),
(null),
(null),
(null),
(null),
(null),
(null),
(null),
(20),
(null),
(null),
(null),
(null),
(30),
(null),
(40),
(null),
(null),
(50)


select 
    t.RowNumber
    ,OldVal =   t.Value
    ,NewVal =   case 
                    when t.[Value] is null 
                        then (select t3.[Value] 
                              from #YourTable t3 
                              where t3.RowNumber = (select max(RowNumber) 
                                                    from #YourTable t2 
                                                    where t2.RowNumber < t.RowNumber and t2.Value is not null)
                             ) 
                    else [Value] 
                end
from #YourTable t
order by
    t.RowNumber

drop table #YourTable

如果您要更新表格，请按以下步骤操作（新测试数据）。

create table #YourTable (RowNumber int identity(1,1), [Value] int null)
insert into #YourTable 
values
(10),
(null),
(null),
(null),
(5),
(null),
(null),
(null),
(20),
(null),
(15),
(null),
(null),
(30),
(null),
(40),
(null),
(null),
(50),
(null),
(null)

update t
set  [Value] =  case 
                    when t.[Value] is null 
                        then (select t3.[Value] 
                              from #YourTable t3 
                              where t3.RowNumber = (select max(RowNumber) 
                                                    from #YourTable t2 
                                                    where t2.RowNumber < t.RowNumber and t2.Value is not null)
                             ) 
                    else [Value] 
                end
from #YourTable t


select * from #YourTable order by RowNumber

一旦更新了表，那么insert语句只需要检查是否插入IS NULL的值，如果是，则将其设置为最后一个值。那会是这样的......

这里我们插入一个NULL，因此插入的值实际上将基于最后一个测试表50

declare @valToInsert int = null
insert into #YourTable
select case when @valToInsert is null then (select top 1 [Value] from #YourTable order by RowNumber desc) else @valToInsert end

然后，由于我们没有在下面插入NULL，它将插入实际值

declare @valToInsert int = 14
insert into #YourTable
select case when @valToInsert is null then (select top 1 [Value] from #YourTable order by RowNumber desc) else @valToInsert end