Breaking down a date range into multiple rows - sql

Question

Let's say I have a table as follows (multiple projects with multiple date ranges):
Project | Start_Date | End_Date
ABC123 10/19/2018 12/31/2018
Is there a way to query this into a result set that looks like the following?:
Project | Start_Date | End_Date
ABC123 10/19/18 10/31/18
ABC123 11/01/18 11/30/18
ABC123 12/01/18 12/31/18

Answer 1

This might need more optimization but giving output as expected as of now
WITH TEMP1 (PROJECT,START_DATE , END_DATE, DT) AS
(
SELECT PROJECT,START_DATE
,END_DATE
,START_DATE DT
FROM MYTABLE
UNION ALL
SELECT PROJECT
,START_DATE
,END_DATE
,DATEADD(DAY, 1, DT) DT
FROM TEMP1
WHERE DT < END_DATE
)
,TEMP2 AS(
SELECT PROJECT
,DATEADD(MONTH, DATEDIFF(MONTH, 0, DT), 0) STARTDATE
,EOMONTH(DT ) ENDDATE
FROM TEMP1
GROUP BY PROJECT
,DATEADD(MONTH, DATEDIFF(MONTH, 0, DT), 0)
,EOMONTH(DT )
)
SELECT B.PROJECT
,CASE WHEN B.STARTDATE < A.START_DATE THEN A.START_DATE
ELSE B.STARTDATE END AS STARTDATEFINAL
,CASE WHEN B.ENDDATE > A.END_DATE THEN A.END_DATE
ELSE B.ENDDATE END AS ENDDATEFINAL
FROM MYTABLE A, TEMP2 B
WHERE A.PROJECT = B.PROJECT

Answer 2

You can use a recursive CTE:
with cte as (
select project, start_date, eomonth(start_date) as end_date, end_date as final_date
from t
union all
select project, dateadd(day, 1, end_date), eomonth(dateadd(day, 1, end_date)), final_date
from cte
where end_date < final_date
)
select project_start_date, end_date
from cte;
Note that your question is a bit ambiguous about a couple of things. Notably, this assumes:
The end date is not in the same month as the start date.
The end date is always at the end of the month (or equivalently, you always want the end of the month for the last record).
These are consistent with your sample data. It is pretty easy to modify the query to handle these, using conditional logic.
EDIT:
For the conditions in the comment:
with cte as (
select project, start_date,
(case when end_date < eomonth(start_date) then end_date
else eomonth(start_date)
end) as end_date,
end_date an final_date
from t
union all
select project, start_date,
(case when end_date < eomonth(start_date) then end_date
else eomonth(start_date)
end) as end_date,
end_date as final_date
from t
union all
select project, dateadd(day, 1, end_date),
(case when final_date < eomonth(dateadd(day, 1, end_date))
then final_date
else eomonth(dateadd(day, 1, end_date))
end), final_date
from cte
where end_date < final_date
)
select project_start_date, end_date
from cte;
Here is a db<>fiddle.