How to determine the number of days in a month for a given Date Range? - sql

Question

I need to calculate using SQL Query, how many days within a given range fall into each calendar month.
I have given 2 dates, which define a date range; for example 2020-01-01 to 2020-08-03. I need to find how many days in that range fall in to each month i.e. how many fall into July, and how many into August.
In the example given, the expected result is 31 days in July and 3 days in August.

Answer 1

One approach uses a recusive query. Using date artithmetics, we can build the query so it performs one iteration per month rather than one per day, so this should be a rather efficient approach:
with cte as (
select
datefromparts(year(#dt_start), month(#dt_start), 1) month_start,
1 - day(#dt_start) + day(
case when #dt_end > eomonth(#dt_start)
then eomonth(#dt_start)
else #dt_end
end
) as no_days
union all
select
dateadd(month, 1, month_start),
case when #dt_end > dateadd(month, 2, month_start)
then day(eomonth(dateadd(month, 1, month_start)))
else day(#dt_end)
end
from cte
where dateadd(month, 1, month_start) <= #dt_end
)
select * from cte
Demo on DB Fiddle.
If we set the boundaries as follows:
declare #dt_start date = '2020-07-10';
declare #dt_end date = '2020-09-10';
Then the query returns:
month_start | no_days
:---------- | ------:
2020-07-01 | 22
2020-08-01 | 31
2020-09-01 | 10

Answer 2

You can refer this
;with dates(thedate) as (
select dateadd(yy,years.number,0)+days.number
from master..spt_values years
join master..spt_values days
on days.type='p' and days.number < datepart(dy,dateadd(yy,years.number+1,0)-1)
where years.type='p' and years.number between 100 and 150
-- note: 100-150 creates dates in the year range 2000-2050
-- adjust as required
)
select dateadd(m,datediff(m, 0, d.thedate),0) themonth, count(1)
from dates d
where d.thedate between '2020-01-01' and '2020-08-03'
group by datediff(m, 0, d.thedate)
order by themonth;
Please refer the link below where RichardTheKiwi user given a clear example for your scenario.
SQL Server query for total number of days for a month between date ranges

Answer 3

You can do all the work at the month level rather than the day level -- which should be a bit faster. Here is a method using a recursive CTE:
with cte as (
select #startdate as startdate, #enddate as enddate,
datefromparts(year(#startdate), month(#startdate), 1) as month
union all
select startdate, enddate, dateadd(month, 1, month)
from cte
where dateadd(month, 1, month) < #enddate
)
select month,
(case when month <= startdate and dateadd(month, 1, month) >= enddate
then day(enddate) - day(startdate) + 1
when month <= startdate
then day(eomonth(month)) - day(startdate) + 1
when dateadd(month, 1, month) < enddate
then day(eomonth(month))
when dateadd(month, 1, month) >= enddate
then day(enddate)
end)
from cte;
And the db<>fiddle.
The logic is simpler at the day level:
with cte as (
select #startdate as dte, #enddate as enddate
union all
select dateadd(day, 1, dte), enddate
from cte
where dte < enddate
)
select datefromparts(year(dte), month(dte), 1) as yyyymm, count(*)
from cte
group by datefromparts(year(dte), month(dte), 1)
order by yyyymm
option (maxrecursion 0)

Answer 4

Here is a solution with recursive CTE.
declare #startDate date = '2020-07-01'
declare #endDate date = '2020-08-03'
; WITH cte (n, year, month, daycnt)
AS (
SELECT
0
, DATEPART(year, #startDate)
, DATENAME(MONTH, #startDate)
, DATEPART(day, EOMONTH( #startDate ) ) - DATEPART(day, #startDate ) + 1
UNION ALL
SELECT
n + 1
, DATEPART(year, DATEADD(month, n + 1, #startDate) )
, DATENAME(MONTH, DATEADD(month, n + 1, #startDate) )
, IIF(
n = ( DATEPART(month, #endDate) - DATEPART(month, #startDate) ) + ( DATEPART(year, #endDate) - DATEPART(year, #startDate) ) * 12 - 1
, DATEPART(day, #endDate )
, DATEPART(day, EOMONTH( DATEADD(month, n + 1, #startDate) ) )
)
FROM
cte
WHERE
n <= ( DATEPART(month, #endDate) - DATEPART(month, #startDate) ) + ( DATEPART(year, #endDate) - DATEPART(year, #startDate) ) * 12 - 1
)
SELECT *
FROM cte
ORDER BY n
OPTION (maxrecursion 0)
This could be further simplified with a number function but that would also be essentially be a recursive CTE, though it would definitely look cleaner. But it requires defining a function on top of this SELECT statement.