Это позволяет получить ваше изображение:
Настройка тестовых данных
create table #test (CaseNumber int, StartDate date, Enddate date)
insert into #test (CaseNumber, StartDate, Enddate)
values(1,'2019-09-18','2019-09-24'),(2,'2019-09-23',NULL)
Код
;with dt_seq as (
select t.CaseNumber, t.StartDate, isnull(t.Enddate,cast (getdate() as date)) EndDate, t.StartDate [Date]
from #test t
union all
select z.CaseNumber, z.StartDate, z.EndDate, case when z.[Date] < z.EndDate then dateadd(day,1,z.[Date]) else z.EndDate end [Date]
from dt_seq z
where z.[Date] <= dateadd(day,-1,z.EndDate)
)
select c.*, ROW_NUMBER() over (partition by c.CaseNumber order by c.[Date]) [Duration]
from dt_seq c
order by c.CaseNumber, c.[Date]
option ( MaxRecursion 0 )
Reuslts