SQL date range breaking into months - sql-server

Question

I have a sql table that has the following
ID StartDate EndDate
10 2015-12-01 2016-05-31
15 2016-01-05 2016-07-04
20 2016-02-10 2016-08-09
I need to break down the months like so...
ID StartDate EndDate
10 2015-12-01 2015-12-31
10 2016-01-01 2016-01-31
10 2016-02-01 2016-02-29
10 2016-03-01 2016-03-31
10 2016-04-01 2016-04-30
10 2016-05-01 2016-05-31
15 2016-01-05 2016-02-04
15 2016-02-05 2016-03-04
15 2016-03-05 2016-04-04
15 2016-04-05 2016-05-04
15 2016-05-05 2016-06-04
15 2016-06-05 2016-07-04
etc
I'm new to SQL so an example would be very helpful

Answer 1

Calendar
recommended if you have persistent Calendar/DateRanges table
declare #datebegin date = '20140101'
;with cteCalendar as
(
select
c.period_start,
dateadd(dd, -1, dateadd(mm, 1, c.period_start)) as period_end
from
(
select top 100
dateadd(mm, row_number() over(order by sc.object_id)-1, #datebegin) as period_start
from sys.columns sc
order by period_start
) c
),
cteData as
(
select cast(10 as int) as id, cast('20151201' as date) as StartDate, cast('20160531' as date) as EndDate
union all
select 15, '20160105', '20160704'
union all
select 25, '20160210', '20160809'
),
cteDataEx as
(
select d.id, d.StartDate, d.EndDate, datepart(dd, d.StartDate)-1 as DateOffset
from cteData d
)
select
d.id,
dateadd(dd, d.DateOffset, c.period_start) as StartDate,
dateadd(dd, d.DateOffset, c.period_end) as EndDate
from cteDataEx d
inner join cteCalendar c on c.period_start <= d.EndDate and c.period_end >= d.StartDate
where dateadd(dd, d.DateOffset, c.period_end) <= d.EndDate
order by id, StartDate
Actually I did not notice at the beginning that periods may start and end not at 1st day of month, so had to append some calculations after completion of the whole script. Later I realized that <= >= date filter produces unnecessary last row which overflows original date range high bound. So had to append final filter and after that modification don't like this approach totally )) May be some enhancements can be applied but I'm not interested in. Lots of ways to accomplish this task. Additional information about nature and purpose of periods given may alter relevance and applicability of different approaches
Recursion
no extra data required but recursion can be slow if date ranges can be wide enough.
;with cteData as
(
select cast(10 as int) as id, cast('20151201' as date) as StartDate, cast('20160531' as date) as EndDate
union all
select 15, '20160105', '20160704'
union all
select 25, '20160210', '20160809'
),
ctePeriods as
(
select
d.id,
d.StartDate,
dateadd(dd, -1, dateadd(mm, 1, d.StartDate)) as EndDate,
d.EndDate as _EndDate
from cteData d
union all
select
p.id,
dateadd(mm, 1, p.StartDate),
dateadd(dd, -1, dateadd(mm, 2, p.StartDate)),
p._EndDate
from ctePeriods p
where p.EndDate < p._EndDate
)
select p.id, p.StartDate, p.EndDate
from ctePeriods p
order by id, startdate

Answer 2

this code generate the rage of months, inclute leap year, but I don't undestand your need so explain better
create table #dia_meses
(mes int,
messtr varchar(2),
dia_final varchar(2))
insert into #dia_meses values(1,'01','31')
insert into #dia_meses values(2,'02','29')
insert into #dia_meses values(3,'03','31')
insert into #dia_meses values(4,'04','30')
insert into #dia_meses values(5,'05','31')
insert into #dia_meses values(6,'06','30')
insert into #dia_meses values(7,'07','31')
insert into #dia_meses values(8,'08','31')
insert into #dia_meses values(9,'09','30')
insert into #dia_meses values(10,'10','31')
insert into #dia_meses values(11,'11','30')
insert into #dia_meses values(12,'12','31')
declare #year varchar(4)
declare #contador int
set #year =convert(varchar,DATEPART(YEAR,GETDATE()))
set #contador =convert(varchar,DATEPART(month,GETDATE()))
declare #dataIni datetime
declare #datafim datetime
set #dataIni=(select #year+'-'+messtr+'-01' from #dia_meses where mes=#contador)
--pulo do gato ano bissexto
if(#contador=2)
begin
if(select ISDATE(#year+'-'+messtr+'-'+dia_final) from #dia_meses where mes=#contador)=0
begin
set #datafim=(select #year+'-'+messtr+'-28' from #dia_meses where mes=#contador)
end
else--ano bissexto
begin
set #datafim=(select #year+'-'+messtr+'-'+dia_final from #dia_meses where mes=#contador)
end
end
else
begin
set #datafim=(select #year+'-'+messtr+'-'+dia_final from #dia_meses where mes=#contador)
end
print #dataIni
print #dataFim

Answer 3

This will work on SQL Server 2012 and up; the EOMONTH function does not exist on earlier versions.
DECLARE #table TABLE (ID INT, StartDate DATE, EndDate DATE)
DECLARE #outtable TABLE (ID INT, StartDate DATE, EndDate DATE)
DECLARE #ID INT
DECLARE #StartDate DATE
DECLARE #Date1 DATE
DECLARE #Date2 DATE
DECLARE #EndDate DATE
INSERT INTO #table VALUES
(10,'2015-12-01','2016-05-31')
,(15,'2016-01-05','2016-07-04')
,(20,'2016-02-10','2016-08-09')
DECLARE tablecursor CURSOR FOR
SELECT * FROM #table
OPEN tablecursor
FETCH NEXT FROM tablecursor INTO #ID, #StartDate, #EndDate
WHILE ##FETCH_STATUS = 0
BEGIN
SET #Date1 = #StartDate
SET #Date2 = EOMONTH(#Date1)
WHILE #Date1 < #EndDate
BEGIN
PRINT CONVERT(VARCHAR,#ID) + ' ' + CONVERT(VARCHAR,#Date1) + ' ' + CONVERT(VARCHAR,#Date2)
INSERT INTO #outtable
SELECT #ID, #Date1, #Date2
SET #Date1 = DATEADD(DAY,1,#Date2)
SET #Date2 = EOMONTH(#Date1)
IF #Date2 > #EndDate
BEGIN
SET #Date2 = #EndDate
END
END
FETCH NEXT FROM tablecursor INTO #ID, #StartDate, #EndDate
END
SELECT * FROM #outtable
CLOSE tablecursor
DEALLOCATE tablecursor