Splitting dates into intervals using Start Date and End Date - sql

Question

I have scenario where I need to split the given date range into monthly intervals.
For example, the input is like below:
StartDate EndDate
2018-01-21 2018-01-29
2018-01-30 2018-02-23
2018-02-24 2018-03-31
2018-04-01 2018-08-16
2018-08-17 2018-12-31
And the expected output should be like below:
StartDate EndDate
2018-01-21 2018-01-29
2018-01-30 2018-01-31
2018-02-01 2018-02-23
2018-02-24 2018-02-28
2018-03-01 2018-03-31
2018-04-01 2018-04-30
2018-05-01 2018-05-31
2018-06-01 2018-06-30
2018-07-01 2018-07-31
2018-08-01 2018-08-16
2018-08-17 2018-08-31
2018-09-01 2018-09-30
2018-10-01 2018-10-31
2018-11-01 2018-11-30
2018-12-01 2018-12-31
Below is the sample data.
CREATE TABLE #Dates
(
StartDate DATE,
EndDate DATE
);
INSERT INTO #Dates
(
StartDate,
EndDate
)
VALUES
('2018-01-21', '2018-01-29'),
('2018-01-30', '2018-02-23'),
('2018-02-24', '2018-03-31'),
('2018-04-01', '2018-08-16'),
('2018-08-17', '2018-12-31');

Answer 1

You can use a recursive CTE. The basic idea is to start with the first date 2018-01-21 and build a list of all months' start and end date upto the last date 2018-12-31. Then inner join with your data and clamp the dates if necessary.
DECLARE #Dates TABLE (StartDate DATE, EndDate DATE);
INSERT INTO #Dates (StartDate, EndDate) VALUES
('2018-01-21', '2018-01-29'),
('2018-01-30', '2018-02-23'),
('2018-02-24', '2018-03-31'),
('2018-04-01', '2018-08-16'),
('2018-08-17', '2018-12-31');
WITH minmax AS (
-- clamp min(start date) to 1st day of that month
SELECT DATEADD(MONTH, DATEDIFF(MONTH, CAST('00010101' AS DATE), MIN(StartDate)), CAST('00010101' AS DATE)) AS mindate, MAX(EndDate) AS maxdate
FROM #Dates
), months AS (
-- calculate first and last day of each month
-- e.g. for February 2018 it'll return 2018-02-01 and 2018-02-28
SELECT mindate AS date01, DATEADD(DAY, -1, DATEADD(MONTH, 1, mindate)) AS date31, maxdate
FROM minmax
UNION ALL
SELECT DATEADD(MONTH, 1, prev.date01), DATEADD(DAY, -1, DATEADD(MONTH, 2, prev.date01)), maxdate
FROM months AS prev
WHERE prev.date31 < maxdate
)
SELECT
-- clamp start and end date to first and last day of corresponding month
CASE WHEN StartDate < date01 THEN date01 ELSE StartDate END,
CASE WHEN EndDate > date31 THEN date31 ELSE EndDate END
FROM months
INNER JOIN #Dates ON date31 >= StartDate AND EndDate >= date01
If rCTE is not an option you can always JOIN with a table of numbers or table of dates (the idea above still applies).

Answer 2

You can Cross Apply with the Master..spt_values table to get a row for each month between StartDate and EndDate.
SELECT *
into #dates
FROM (values
('2018-01-21', '2018-01-29')
,('2018-01-30', '2018-02-23')
,('2018-02-24', '2018-03-31')
,('2018-04-01', '2018-08-16')
,('2018-08-17', '2018-12-31')
)d(StartDate , EndDate)
SELECT
SplitStart as StartDate
,case when enddate < SplitEnd then enddate else SplitEnd end as EndDate
FROM #dates d
cross apply (
SELECT
cast(dateadd(mm, number, dateadd(dd, (-datepart(dd, d.startdate) +1) * isnull((number / nullif(number, 0)), 0), d.startdate)) as date) as SplitStart
,cast(dateadd(dd, -datepart(dd, dateadd(mm, number+1, startdate)), dateadd(mm, number+1, startdate)) as date) as SplitEnd
FROM
master..spt_values
where type = 'p'
and number between 0 and (((year(enddate) - year(startdate)) * 12) + month(enddate) - month(startdate))
) s
drop table #dates

Answer 3

The following should also work
First i put startdates and enddates into a single column in the cte-block data.
In the block som_eom, i create the start_of_month and end_of_month for all 12 months.
I union steps 1 and 2 into curated_set
I create curated_set which is ordered by the date column
Finally i reject the unwanted records, in my filter clause not in('som','StartDate')
with data
as (select *
from dates
unpivot(x for y in(startdate,enddate))t
)
,som_eom
as (select top 12
cast('2018-'+cast(row_number() over(order by (select null)) as varchar(2))+'-01' as date) as som
,dateadd(dd
,-1
,dateadd(mm
,1
,cast('2018-'+cast(row_number() over(order by (select null)) as varchar(2))+'-01' as date)
)
) as eom
from information_schema.tables
)
,curated_set
as(select *
from data
union all
select *
from som_eom
unpivot(x for y in(som,eom))t
)
,curated_data
as(select x
,y
,lag(x) over(order by x) as prev_val
from curated_set
)
select prev_val as st_dt,x as end_dt
,y
from curated_Data
where y not in('som','StartDate')

Answer 4

Start with the initial StartDate and calculate the end of month or simply use the EndDate if it's within the same month.
Use the newly calculated EndDate+1 as StartDate for recursion and repeat the calculation.
WITH cte AS
( SELECT StartDate, -- initial start date
CASE WHEN EndDate < DATEADD(DAY,-1,DATEADD(MONTH, DATEDIFF(MONTH,0,StartDate)+1,0))
THEN EndDate
ELSE DATEADD(DAY,-1,DATEADD(MONTH, DATEDIFF(MONTH,0,StartDate)+1,0))
END AS newEnd, -- LEAST(end of current month, EndDate)
EndDate
FROM #Dates
UNION ALL
SELECT dateadd(DAY,1,newEnd), -- previous end + 1 day, i.e. 1st of current month
CASE WHEN EndDate <= DATEADD(DAY,-1,DATEADD(MONTH, DATEDIFF(MONTH,0,StartDate)+2,0))
THEN EndDate
ELSE DATEADD(DAY,-1,DATEADD(MONTH, DATEDIFF(MONTH,0,StartDate)+2,0))
END, -- LEAST(end of next month, EndDate)
EndDate
FROM cte
WHERE newEnd < EndDate
)
SELECT StartDate, newEnd
FROM cte