How to get Previous Value for Null Values

Question

I have the Below Data in my Table.

   | 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  |

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  |

Answer 1

Since you are on SQL Server 2012... here is a version that uses that. It might be faster than other solutions but you have to test that on your data.

sum() over() will do a running sum ordered by Id adding 1 when there are a value in the column and keeping the current value for null values. The calculated running sum is then used to partition the result in first_value() over(). The first value ordered by Id for each "group" of rows generated by the running sum has the value you want.

select T.Id,
       first_value(T.FeeModeId) 
          over(partition by T.NF 
               order by T.Id 
               rows between unbounded preceding and current row) as FeeModeId,
       first_value(T.Name)      
          over(partition by T.NS 
               order by T.Id 
               rows between unbounded preceding and current row) as Name,
       T.Amount
from (
     select Id,
            FeeModeId,
            Name,
            Amount,
            sum(case when FeeModeId is null then 0 else 1 end) 
              over(order by Id) as NF,
            sum(case when Name is null then 0 else 1 end) 
              over(order by Id) as NS
     from YourTable
     ) as T

SQL Fiddle

Something that will work pre SQL Server 2012:

select T1.Id,
       T3.FeeModeId,
       T2.Name,
       T1.Amount
from YourTable as T1
  outer apply (select top(1) Name
               from YourTable as T2
               where T1.Id >= T2.Id and
                     T2.Name is not null
               order by T2.Id desc) as T2
  outer apply (select top(1) FeeModeId
               from YourTable as T3
               where T1.Id >= T3.Id and
                     T3.FeeModeId is not null
               order by T3.Id desc) as T3

SQL Fiddle

Answer 2

Please try:

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

OR

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