SQL query group by using day startdatetime and end datetime - sql

Question

I have the following table Jobs:
|Id | StartDateTime | EndDateTime
+----+---------------------+----------------------
|1 | 2020-10-20 23:00:00 | 2020-10-21 05:00:00
|2 | 2020-10-21 10:00:00 | 2020-10-21 11:00:00
Note job id 1 spans October 20 and 21.
I am using the following query
SELECT DAY(StartDateTime), COUNT(id)
FROM Job
GROUP BY DAY(StartDateTime)
To get the following output. But the problem I am facing is that day 21 is not including job id 1. Since the job spans two days I want to include it in both days 20 and 21.
Day | TotalJobs
----+----------
20 | 1
21 | 1
I am struggling to get the following expected output:
Day | TotalJobs
----+----------
20 | 1
21 | 2

Answer 1

One method is to generate the days that you want and then count overlaps:
with days as (
select convert(date, min(j.startdatetime)) as startd,
convert(date, max(j.enddatetime)) as endd
from jobs j
union all
select dateadd(day, 1, startd), endd
from days
where startd < endd
)
select days.startd, count(j.id)
from days left join
jobs j
on j.startdatetime < dateadd(day, 1, startd) and
j.enddatetime >= startd
group by days.startd;
Here is a db<>fiddle.

Answer 2

You can first group by with same start and end date and then group by for start and end date having different start and end date
SELECT a.date, SUM(counts) from (
SELECT DAY(StartDateTime) as date, COUNT(id) counts
FROM Table1
WHERE DAY(StartDateTime) = DAY(EndDateTime)
GROUP BY StartDateTime
UNION ALL
SELECT DAY(EndDateTime), COUNT(id)
FROM Table1
WHERE DAY(StartDateTime) != DAY(EndDateTime)
GROUP BY EndDateTime
UNION ALL
SELECT DAY(StartDateTime), COUNT(id)
FROM Table1
WHERE DAY(StartDateTime) != DAY(EndDateTime)
GROUP BY StartDateTime) a
GROUP BY a.date
Here is SQL Fiddle link
SQL Fiddle
Also replace Table1 with Jobs when running over your db context