split the date range by every 6 months dynamically. Start date can be any thing, but add up to month range - sql

Question

Please help to split the date range by every 6 moths and the start date could be anything but using the start date we need to add up to 09-30 only and the next day which is 10/01 should become start date. I tried using recursive cte but still not getting the exact result
startdate enddate
06-22-2018 09-30-2022
output
startdate enddate
06-22-2018 09-30-2018
10-01-2018 03-31-2019
04-01-2019 09-30-2019
10-01-2019 03-31-2020
04-01-2020 09-30-2020

Answer 1

Here is another option which uses an ad-hoc tally table
Example
Declare #YourTable table (startdate date, enddate date)
Insert Into #YourTable values
('06/22/2018','09/30/2022')
;with cte as (
Select *
,Grp = sum( case when day(D)=1 and month(D) in (4,10) then 1 else 0 end) over (order by d)
From #YourTable A
Cross Apply (
Select Top (DateDiff(DAY,startdate,enddate)+1) D=DateAdd(DAY,-1+Row_Number() Over (Order By (Select Null)),startdate)
From master..spt_values n1,master..spt_values n2
) B
)
Select StartDate = min(D)
,EndDate = max(D)
From cte
Group by Grp
Order By min(D)
Returns
StartDate EndDate
2018-06-22 2018-09-30
2018-10-01 2019-03-31
2019-04-01 2019-09-30
2019-10-01 2020-03-31
2020-04-01 2020-09-30
2020-10-01 2021-03-31
2021-04-01 2021-09-30
2021-10-01 2022-03-31
2022-04-01 2022-09-30
Option where we JOIN to an ad-hoc calendar table (note the TOP 10000 and base date of 2000-01-01)
Declare #YourTable table (id int,startdate date, enddate date)
Insert Into #YourTable values
(1,'06/22/2018','09/30/2022')
;with cte as (
Select A.*
,B.D
,Grp = sum( case when day(D)=1 and month(D) in (4,10) then 1 else 0 end) over (order by d)
From #YourTable A
Join (
Select Top 10000 D=DateAdd(DAY,-1+Row_Number() Over (Order By (Select Null)),'2000-01-01')
From master..spt_values n1,master..spt_values n2
) B on D between startDate and EndDate
and (D in (startdate,EndDate)
or ( day(D) in (1,day(eomonth(d))) and month(D) in (3,4,9,10))
)
)
Select ID
,StartDate = min(D)
,EndDate = max(D)
From cte
Group by ID,Grp
Order By ID,min(D)
Returns
ID StartDate EndDate
1 2018-06-22 2018-09-30
1 2018-10-01 2019-03-31
1 2019-04-01 2019-09-30
1 2019-10-01 2020-03-31
1 2020-04-01 2020-09-30
1 2020-10-01 2021-03-31
1 2021-04-01 2021-09-30
1 2021-10-01 2022-03-31
1 2022-04-01 2022-09-30

Answer 2

You can use a recursive CTE:
with cte as (
select startdate, eomonth(datefromparts(year(startdate), 9, 1)) as enddate, enddate as orig_enddate
from t
union all
select dateadd(day, 1, enddate), eomonth(dateadd(month, 5, dateadd(day, 1, enddate))) as enddate, orig_enddate
from cte
where enddate < orig_enddate
)
select *
from cte;
Here is a db<>fiddle.
It is unclear what year you want for the first row. As per your question, this uses Sep 30th of the year of the startdate.
If you need more than 100 dates, then add option max(recursion 0).