Find number of days that intersect a given date range in a table of date ranges - sql

Question

I want to find the total number of days in a date range that overlap a table of date ranges.
For example, I have 7 days between 2 dates in the table below. I want to find the days between between them that also fall this date range: 2019-08-01 to 2019-08-30.
It should return 1 day.
This is the data source query:
SELECT LeaveId, UserId, StartDate, EndDate, Days
FROM TblLeaveRequest
WHERE UserId = 218
LeaveID UserID StartDate EndDate Days
----------- ----------- ----------------------- ----------------------- -----------
22484 218 2019-07-26 00:00:00.000 2019-08-01 00:00:00.000 7

Answer 1

I believe this might help you:
--create the table
SELECT
22484 LeaveID,
218 UserID,
CONVERT(DATETIME,'7/26/2019') StartDate,
CONVERT(DATETIME,'8/1/2019') EndDate,
7 Days
INTO #TblLeaveRequest
--Range Paramters
DECLARE #StartRange AS DATETIME = '8/1/2019'
DECLARE #EndRange AS DATETIME = '8/30/2019'
--Find sum of days between StartDate and EndDate that intersect the range paramters
--for UserId=218
SELECT
SUM(
DATEDIFF(
DAY
,CASE WHEN #StartRange < StartDate THEN StartDate ELSE #StartRange END
,DATEADD(DAY, 1, CASE WHEN #EndRange > EndDate THEN EndDate ELSE #EndRange END)
)
) TotalDays
from #TblLeaveRequest
where UserId=218
This assumes that no start dates are greater than end dates. It also assumes that the range parameters always intersect some portion of the range in the table.
If the parameter ranges might not intersect then you'll have to eliminate those cases by excluding negative days:
SELECT SUM( CASE WHEN Days < 0 THEN 0 ELSE Days END ) TotalDays
FROM
(
SELECT
DATEDIFF(
DAY
,CASE WHEN #StartRange < StartDate THEN StartDate ELSE #StartRange END
,DATEADD(DAY, 1, CASE WHEN #EndRange > EndDate THEN EndDate ELSE #EndRange END)
) Days
from #TblLeaveRequest
where UserId=218
) TotalDays

Answer 2

if I understand your problem correctly, you have two ranges of dates and you are looking for the number of days in the intersection.
Considering a Gant chart:
Start_1 .................... End_1
Start_2 .......................End_2
If you can create a table structure like
LeaveID UserID StartDate_1 EndDate_1 StartDate_2 EndDate_2
----------- ----------- ---------- --------- ---------- ---------
22484 218 2019-07-26 2019-08-01 2019-08-01 2019-08-30
You can determine the number of days by
select
leaveID
, UserID
,case
when StartDate_2 <= EndDate_1 then datediff(day,StartDate_2,EndDate_1) + 1
else 0
end as delta_days_intersection
from table
I hope that helps

Answer 3

You can use a numbers (Tally) table to count the number of days:
SQL Fiddle
MS SQL Server 2017 Schema Setup:
CREATE TABLE LeaveRequest
(
LeaveId Int,
UserId Int,
StartDate Date,
EndDate Date,
Days Int
)
Insert Into LeaveRequest
VALUES
(22484, 218, '2019-07-26','2019-08-01', 7)
Query 1:
DECLARE #StartDate Date = '2019-08-01'
DECLARE #EndDate Date = '2019-08-30'
;WITH Tally
AS
(
SELECT ROW_NUMBER() OVER (ORdER By Numbers.Num) AS Num
FROM
(
Values(1),(2),(3),(4),(5),(6),(7),(8),(9)
)Numbers(Num)
Cross APPLY
(
Values(1),(2),(3),(4),(5),(6),(7),(8),(9)
)Numbers2(Num2)
)
SELECT COUNT(DATEADD(d, Num -1, StartDate)) As NumberOfDays
FROM LeaveRequest
CROSS APPLY Tally
WHERE DATEADD(d, Num -1, StartDate) <= EndDate AND
DATEADD(d, Num -1, StartDate) >= #StartDate AND
DATEADD(d, Num -1, StartDate) <= #EndDate
Results:
| NumberOfDays |
|--------------|
| 1 |

Answer 4

CREATE TABLE #LeaveRequest
(
LeaveId Int,
UserId Int,
StartDate Date,
EndDate Date,
Days Int
)
Insert Into #LeaveRequest
VALUES
(22484, 218, '2019-07-26','2019-08-01', 7)
Declare #FromDate datetime='2019-08-01'
declare #ToDate datetime='2019-08-30'
;With CTE as
(
select top (DATEDIFF(day,#FromDate,#ToDate)+1)
DATEADD(day, ROW_NUMBER()over(order by (select null))-1,#FromDate) DT
from sys.objects
)
select * from #LeaveRequest LR
cross apply(select count(*)IntersectingDays
from CTE c where dt between lr.StartDate and lr.EndDate)ca
--or
--select lr.*,c.*
from CTE c
--cross apply
(select lr.* from #LeaveRequest LR
where c.DT between lr.StartDate and lr.EndDate)lr
drop table #LeaveRequest
Better create one Calendar table which will always help you in other queries also.
create table CalendarDate(Dates DateTime primary key)
insert into CalendarDate WITH (TABLOCK) (Dates)
select top (1000000)
DATEADD(day, ROW_NUMBER()over(order by (select null))-1,'1970-01-01') DT
from sys.objects
Then inside CTE write this,
select top (DATEDIFF(day,#FromDate,#ToDate)+1) Dates from CalendarDate
where Dates between #FromDate and #ToDate

Answer 5

DECLARE #FromDate datetime = '2019-08-01'
DECLARE #ToDate datetime = '2019-08-30'
SELECT
IIF(#FromDate <= EndDate AND #ToDate >= StartDate,
DATEDIFF(day,
IIF(StartDate > #FromDate, StartDate, #FromDate),
IIF(EndDate < #ToDate, EndDate, #ToDate)
),
0) AS overlapping_days
FROM TblLeaveRequest;