如何获取空值的先前值 [英] How to get Previous Value for Null Values

问题描述

我的表中有以下数据.

   | Id  |  FeeModeId   |Name        |   Amount|
   ---------------------------------------------
   | 1   |  NULL        | NULL       |   20    |
   | 2   |  1           | Quarter-1  |   5000  |
   | 3   |  NULL        | NULL       |   2000  |    
   | 4   |  2           | Quarter-2  |   8000  |
   | 5   |  NULL        | NULL       |   5000  |
   | 6   |  NULL        | NULL       |   2000  |
   | 7   |  3           | Quarter-3  |   6000  |
   | 8   |  NULL        | NULL       |   4000  |

如何编写这样的查询以获得低于输出...

How to write such query to get below output...

   | Id  |  FeeModeId   |Name        |   Amount|
   ---------------------------------------------
   | 1   |  NULL        | NULL       |   20    |
   | 2   |  1           | Quarter-1  |   5000  |
   | 3   |  1           | Quarter-1  |   2000  |    
   | 4   |  2           | Quarter-2  |   8000  |
   | 5   |  2           | Quarter-2  |   5000  |
   | 6   |  2           | Quarter-2  |   2000  |
   | 7   |  3           | Quarter-3  |   6000  |
   | 8   |  3           | Quarter-3  |   4000  |

推荐答案

请尝试:

select 
    a.ID,
    ISNULL(a.FeeModeId, x.FeeModeId) FeeModeId,
    ISNULL(a.Name, x.Name) Name,
    a.Amount
from tbl a
outer apply
(select top 1 FeeModeId, Name 
    from tbl b 
    where b.ID<a.ID and 
        b.Amount is not null and 
        b.FeeModeId is not null and 
        a.FeeModeId is null order by ID desc)x

或

select 
    ID,
    ISNULL(FeeModeId, bFeeModeId) FeeModeId,
    ISNULL(Name, bName) Name,
    Amount
From(
    select 
        a.ID , a.FeeModeId, a.Name, a.Amount, 
        b.ID bID, b.FeeModeId bFeeModeId, b.Name bName,
        MAX(b.FeeModeId) over (partition by a.ID) mx
    from tbl a left join tbl b on b.ID<a.ID
    and b.FeeModeId is not null
)x 
where bFeeModeId=mx or mx is null

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