SQL to get next not null value in column

问题

How can I get next not null value in column? I have MSSQL 2012 and table with only one column. Like this:

rownum    Orig
------    ----
1         NULL
2         NULL
3         9
4         NULL
5         7
6         4
7         NULL
8         9

and I need this data:

Rownum    Orig    New
------    ----    ----
1         NULL    9
2         NULL    9
3         9       9
4         NULL    7
5         7       7
6         4       4
7         NULL    5
8         9       5

Code to start:

declare @t table (rownum int, orig int);
insert into @t values (1,NULL),(2,NULL),(3,9),(4,NULL),(5,7),(6,4),(7,NULL),(8,9);
select rownum, orig from @t;

回答1:

One method is to use outer apply:

select t.*, t2.orig as newval
from @t t outer apply
     (select top 1 t2.*
      from @t t2
      where t2.id >= t.id and t2.orig is not null
      order by t2.id
     ) t2;

One way you can do this with window functions (in SQL Server 2012+) is to use a cumulative max on id, in inverse order:

select t.*, max(orig) over (partition by nextid) as newval
from (select t.*,
             min(case when orig is not null then id end) over (order by id desc) as nextid
      from @t
     ) t;

The subquery gets the value of the next non-NULL id. The outer query then spreads the orig value over all the rows with the same id (remember, in a group of rows with the same nextid, only one will have a non-NULL value for orig).

来源：https://stackoverflow.com/questions/33553710/sql-to-get-next-not-null-value-in-column