Split date range from a single row into months that are displayed in multiple rows

Question

I have a table with a few million entries, so I need a solution that can work on a bunch of different scenarios as most solutions I have found is only for a few iterations at best.

I have a PERIOD_FROM and a PERIOD_TO status check, aka how long the account has been in this state. It is no problem to split a two month difference but quite a few of the entries are for accounts that have paid in advance so their status will not change for up to 2 years.

The original table simplified looks something like this:

ID          PERIOD_FROM PERIOD_TO   DAYS
---------------------------------------------------------
115052454   02/04/2019  01/04/2021  730
115678935   06/04/2021  05/04/2023  729
119040627   06/04/2021  05/04/2023  729
115005487   01/04/2019  29/03/2021  728
116414279   17/04/2019  09/04/2021  723
116411046   17/04/2019  04/04/2021  718
116693271   24/04/2019  04/04/2021  711
123935704   05/07/2019  29/05/2021  694
119040627   16/05/2019  05/04/2021  690
115976183   02/05/2019  01/03/2021  669

What I have done for the two month difference solution is create a concat as follows:

CASE WHEN CONCAT(DATEPART(YYYY, [PERIOD_FROM]), FORMAT([PERIOD_FROM], 'MM')) = CONCAT(DATEPART(YYYY, [PERIOD_TO]), FORMAT([PERIOD_TO], 'MM'))
    THEN CONCAT(DATEPART(YYYY, [PERIOD_FROM]), FORMAT([PERIOD_FROM], 'MM'))
        ELSE CONCAT(DATEPART(YYYY, [PERIOD_FROM]), FORMAT([PERIOD_FROM], 'MM'), ',', DATEPART(YYYY, [PERIOD_TO]), FORMAT([PERIOD_TO], 'MM'))
END AS Period_Of

Using cross apply with string_split I can then split the line into two and using another case statement I can assign the full values based on if the period from/to is equal or greater than the split value, but this only works for a two month difference and I need up to 48 months.

I require an output that would look something like this:

ID          PERIOD_FROM PERIOD_TO   DAYS
------------------------------------------------------
1150524545  02/04/2019  30/04/2019  730
1150524545  01/05/2019  31/05/2019  730
1150524545  01/06/2019  30/06/2019  730
1150524545  01/07/2019  31/07/2019  730
   …………            …………             …………    ……
1150524545  01/02/2021  28/02/2021  730
1150524545  01/03/2021  31/03/2021  730
1150524545  01/04/2021  01/04/2021  730

Any help would be greatly appreciated!

---

UPDATE:

Thanks to the help of Serg, I have a solution. I tweaked it slightly so that the Period_To ends on the last date but had not specified that in my request as it was not a main concern.

Answer 1

Using table of numbers

-- Generate table of 1000 numbers starting 0
with t0(n) as (
 select n 
 from (
    values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10)
    ) t(n)
),nmbs as(
   select row_number() over(order by t1.n) - 1 n
   from t0 t1, t0 t2, t0 t3
)
--
select Id
  , dateadd(mm, nmbs.n, tbl.PERIOD_FROM) PERIOD_FROM
  , case when ys.NextDate > tbl.PERIOD_TO then tbl.PERIOD_TO else ys.NextDate end PERIOD_TO
  , DAYS
  , tbl.PERIOD_TO originalPERIOD_TO
from [my table] tbl
join nmbs
on dateadd(mm, nmbs.n, tbl.PERIOD_FROM) <= tbl.PERIOD_TO
cross apply (select  dateadd(mm, nmbs.n + 1, tbl.PERIOD_FROM) NextDate) ys
order by ID, dateadd(mm, nmbs.n, tbl.PERIOD_FROM);

Fiddle