Query to identify contiguous ranges - sql-server

Question

I'm trying to write a query on the below data set to add a new column which has some sort of "period_id_group".
contiguous new_period row_nr new_period_starting_id
0 0 1 0
1 1 2 2
1 0 3 0
1 0 4 0
1 1 5 5
1 0 6 0
What I'm trying to get is:
contiguous new_period row_nr new_period_starting_id period_id_group
0 0 1 0 0
1 1 2 2 2
1 0 3 0 2
1 0 4 0 2
1 1 5 5 5
1 0 6 0 5
The logic is that for each 0 value in the new_period_starting_id, it has to get the >0 value from the row above.
So, for row_nr = 1 since there is no row before it, period_id_group is 0.
For row_nr = 2 since this is a new perid (marked by new_period = 1), the period_id_group is 2 (the id of this row).
For row_nr = 3 since it's part of a contiguous range (because contiguous = 1), but is not the start of the range, because it's not a new_period (new_period = 0), its period_id_group should inherit the value from the previous row (which is the start of the contiguous range) - in this case period_id_group = 2 also.
I've tried multiple versions but couldn't get a good solution for SQL Server 2008R2, since I can't use LAG().
What I have, so far, is a shameful:
select *
from #temp2 t1
left join (select distinct new_period_starting_id from #temp2) t2
on t1.new_period_starting_id >= t2.new_period_starting_id
where 1 = case
when contiguous = 0
then 1
when contiguous = 1 and t2.new_period_starting_id > 0
then 1
else 1
end
order by t1.rn
Sample data script:
declare #tmp2 table (contiguous int
, new_period int
, row_nr int
, new_period_starting_id int);
insert into #tmp2 values (0, 0, 1, 0)
, (1, 1, 2, 2)
, (1, 0, 3, 0)
, (1, 0, 4, 0)
, (1, 1, 5, 5)
, (1, 0, 6, 0);
Any help is appreciated.

Answer 1

So, if I'm understanding you correctly, you just need one additional column.
SELECT t1.contiguous, t1.new_period, t1.row_nr, t1.new_period_starting_id,
(SELECT TOP 1 (new_period_starting_id)
FROM YourTable t2
WHERE t2.row_nr <= t1.row_nr
AND t2.period_id_group > 0 /* optimization */
ORDER BY t2.row_nr DESC /* optimization */) AS period_id_group
FROM YourTable t1

Answer 2

Here is yet another option for this.
select t1.contiguous
, t1.new_period
, t1.row_nr
, t1.new_period_starting_id
, x.new_period_starting_id
from #tmp2 t1
outer apply
(
select top 1 *
from #tmp2 t2
where (t2.row_nr = 1
or t2.new_period_starting_id > 0)
and t1.row_nr >= t2.row_nr
order by t2.row_nr desc
) x

Answer 3

Found the solution:
select *
, case
when contiguous = 0
then f1
when contiguous = 1 and new_periods = 1
then f1
when contiguous = 1 and new_periods = 0
then v
else NULL
end [period_group]
from (
select *
, (select max(f1) from #temp2 where new_period_starting_id > 0 and rn < t1.rn) [v]
from #temp2 t1
) rs
order by rn