DECLARE @t TABLE (ID int, DocRef int, DocValue int, DocValue2 int)
INSERT INTO @t (ID, DocRef, DocValue, DocValue2)
VALUES (812402,2404,13, NULL),
(1012499, 9528, 23, NULL),
(1145396, 14647, 34, NULL),
(1361324, 22846, 54, NULL),
(1365357, 22991, 55, NULL);

select * from @t

DECLARE @ID int
DECLARE @i int = 1

SELECT @ID = MIN(ID) FROM @t

WHILE  @@ROWCOUNT > 0
BEGIN
   UPDATE @t SET DocValue2 = @i WHERE ID = @ID 
   SET @i = @i + 1   

   SELECT TOP 1 @ID = ID FROM @t WHERE ID > @ID ORDER BY ID
END 
select * from @t

DECLARE @t TABLE (ID int, DocRef int, DocValue int, DocValue2 int)
INSERT INTO @t (ID, DocRef, DocValue, DocValue2)
VALUES (812402,2404,13, NULL),
(1012499, 9528, 23, NULL),
(1145396, 14647, 34, NULL),
(1361324, 22846, 54, NULL),
(1365357, 22991, 55, NULL);

declare @x int, @xx int

set @xx=1

DECLARE UpdCol CURSOR  FOR
SELECT ID
FROM @t
order by 1

OPEN UpdCol

FETCH NEXT FROM UpdCol INTO @x

WHILE @@FETCH_STATUS = 0
BEGIN
update @t
set DocValue2 = @xx
where ID=@x

set @xx = @xx + 1

FETCH NEXT FROM UpdCol INTO @x
END
CLOSE UpdCol
DEALLOCATE UpdCol

select * from @t
order by id