Loop Through Recordset and count if Within Date Range - sql

Question

Please note - this is my first post, so I apologize for anything I have missed.
I have a large event table that has a record for each time someone moves within a facility. What I would like to do, is say if that person was in the facility over the previous 365 days, count them (for each day). Essentially, I need the Average Daily Population (for everyone in the facility over the previous 365 days).
thank you.
Example Data:
PersonID ArriveDt LeaveDt Location
1111 1/1/2019 1/3/2019 ABC
1122 1/1/2019 1/5/2019 ABC
1123 1/2/2019 1/6/2019 ABC
Date Count
1/1/2019 2
1/2/2019 3
1/3/2019 3
1/4/2019 2
1/5/2019 2
1/6/2019 1

Answer 1

If you don't care about the intermediate values then really you just need to compute the total man-days and divide.
select sum(datediff(day, adjusted_start, adjusted_end) + 1) / 365.0
from T
cross apply (
select
dateadd(day, -365, cast(getdate() as date)),
dateadd(day, -1, cast(getdate() as date))
) d(range_start, range_end)
cross apply (
select
case when ArriveDt < range_start then range_start else ArriveDt end,
case when LeaveDt > range_end then range_end else LeaveDt end
) a(adjusted_start, adjusted_end);
If not, then come up with a table of dates (from any of numerous sources around the internet) and join from that. An outer join allows for dates with zero census.
with dates as (
select dt from calendar -- exercise for the reader
where
dt >= dateadd(day, -365, cast(getdate() as date)),
and dt <= dateadd(day, -1, cast(getdate() as date))
)
select d.dt, count(*)
from dates d left outer join T t
on d.dt between t.ArriveDt and t.LeaveDt
group by d.dt;

Answer 2

Create basic calendar table for the last X days:
IF OBJECT_ID('tempdb..#Calendar') IS NOT NULL
DROP TABLE #Calendar;
GO
DECLARE #StartDate DATE = DATEADD(d, -365, GETDATE())
DECLARE #EndDate DATE = GETDATE()
CREATE TABLE #Calendar
(
[CalendarDate] DATE
)
WHILE #StartDate <= #EndDate
BEGIN
INSERT INTO #Calendar
(
CalendarDate
)
SELECT
#StartDate
SET #StartDate = DATEADD(dd, 1, #StartDate)
END
GO
Now CROSS JOIN with Calendar Table to get rows per Person per day they were at a Location and the GROUP BY
SELECT
c.CalendarDate
,Location
,COUNT(PersonID) AS PersonCount
FROM (
SELECT PersonID ,ArriveDt ,LeaveDt ,Location FROM dbo.Table
) t
CROSS JOIN Calendar c
WHERE c.CalendarDate BETWEEN t.ArriveDt AND t.LeaveDt
GROUP BY
c.CalendarDate
,Location
Edit (2019-10-08):
If you're unable to create tables, you can use temp tables instead and do a DROP IF EXISTS. You can run both of these parts in one go on the fly to generate your final report.