declare @t table (id int, value int, number int)
insert @t select 12, 17, 13 union all select 13, 34, 17 union all select 14, 5, 19

declare @t table (id int, value int, number int)
insert @t select 12, 17, 13 union all select 13, 34, 17 union all select 14, 5, 19

;with a as (
  select 1 [min_num], max(number) [max_num] from @t
  union all
  select min_num + 1, max_num from a where min_num < max_num
)
select isnull(f.value,0) [value], a.min_num [number]
from a
left join @t t on a.min_num = t.number
outer apply (select top 1 value from @t where number <= a.min_num order by number desc) f

declare @t table (id int, value int, number int)
insert @t select 12, 17, 13 union all select 13, 34, 17 union all select 14, 5, 19

;with cte as (
select *, ROW_NUMBER() over (order by id) as rn
from @t)

,cte_map as(
select isnull(t2.number, 1) as from_, isnull(t1.number - 1, t2.number) as to_, isnull(t2.value, 0) as val_
from cte t1 full join cte t2 on t1.rn = t2.rn + 1)

,c50 as(
select number
from master..spt_values
where type = 'P' and number between 1 and 50)

select t2.val_, t1.number
from c50 t1 inner join cte_map t2 on t1.number between t2.from_ and t2.to_