Question

To maintain my purity and honor as a database dork, I wish to update a set of datetimes and floats that has some nulls in the float column such that each null value will be replaced by the previous (by datetime) non-null value.

My environment is mssql 2k8R2.

I hope the following snippet explains my victory conditions sufficiently.

Cheers and Thanks.

create table #datesAndValues(
    [Date] datetime,
    Val float);
create table #resultsShouldLookLikeThis(
    [Date] datetime,
    Val float);

insert into #datesAndValues 
values  
    ('1/8/11',1.1),
    ('1/7/11',null),
    ('1/6/11',1.2),
    ('1/5/11',null),
    ('1/4/11',null),
    ('1/3/11',1.3),
    ('1/2/11',null),
    ('1/1/11',null);

/*  
    set based code (no loops!!!) goes here to set nulls
    in the above table to the last known good (not null) value,
    thereby making it look like the following table.
*/

insert into #resultsShouldLookLikeThis
values  
    ('1/8/11',1.1),
    ('1/7/11',1.2),
    ('1/6/11',1.2),
    ('1/5/11',1.3),
    ('1/4/11',1.3),
    ('1/3/11',1.3),
    ('1/2/11',null),
    ('1/1/11',null);

--this will tell us if it worked
select 'In old but not new' as [WhichTable], o.*
from    (select * from #datesAndValues
        except select * from #resultsShouldLookLikeThis) o
union all
select 'In new but not old' as [WhichTable], n.*
from    (select * from #resultsShouldLookLikeThis
        except select * from #datesAndValues) n;

drop table #datesAndValues;
drop table #resultsShouldLookLikeThis;

Answer 1

update #datesAndValues set
  Val = (select top 1 Val
         from #datesAndValues as T2
         where
          T2.[Date] < T.[Date] and
          T2.Val is not null
         order by [Date] desc)
from #datesAndValues as T         
where T.Val is null