Is there a way to count days INSIDE a range of dates? - date

Question

I'm quite a beginner on VB/SQL, I just began my learning few months ago, but I can understand the logic of algorithms as I used to do some Excel VBA .
I'm actually designing a database where I can (wish to) follow up every colleague's activity during the year.
The objective is to have a (Monthly) ratio of =>
Billable days / (Billable + Non Billable - Absent)
The context :
A single person can be : Working internally (Non billable), OR Working Externally (Billable) , OR on Holidays (Absent).
I have a [Planning] Table where it stores the following data : [Consultant_ID] (linked to another table [Consultant], [Activity] (A list with the three choices described above), [Beginning_Date], [End_Date].
Example :
Consultant 1 : Working externally from 01/01/2019 to 01/06/2019,
Working internally from 02/06/2019 to 31/12/2019,
Holidays from 02/03/2019 to 15/03/2019
Is there a way to have the Billable ratio of March for example ?
I created 4 queries (Maybe too much ?)
3 queries : [Consultant_ID] [Activity] [Beginning_Date] [End_Date] [Ratio : Datediff("d";[Beginning_Date];[End_Date]).
For each query : The [Activity criteria] : one Working Internally, one Working Externally, one Absent.
And for the [Beginning_Date] and [End_Date] criterias : <=[Enter beginning date], >=[Enter End date]
And the 4th query [Consultant ID] [Billable] [Non billable] [Absent] (and planning to add the [RATIO]).
Problem is : the Datediff counts the dates of the whole activity of what it finds, and not only the dates between 01/03/2019 and 31/03/2019 as I wish to.
I Expect the output of the ratio to be : Billable days / (Billable + Non Billable - Absent) of the desired period.
The actual output shows the billable, non billable, and absent days of the whole period between the dates which are inputted
So instead of 31 Billable, 0 Non billable, 15 Absent
It shows 180 Billable, 0 Non Billable, 32 Absent
Sorry for the long post, it is actually my first, and thank you very much !
I've been struggling with this for a whole week

Answer 1

We first need to figure out the maxBegin and the minEnd dates for each row
SELECT
*,
(IIF (Beginning_Date > #3/1/2019#, Beginning_Date, #3/1/2019#) ) as maxBegin,
(IIF (End_Date < #3/31/2019#, End_Date, #3/31/2019#) ) as minEnd,
Datediff("d", maxBegin, minEnd) + 1 as theDiff
FROM Planning
Where Beginning_Date <= #3/31/2019# AND End_Date >= #3/1/2019#
Then use that to compute the durations. Note: DateDiff does not count both ends, so we need to add +1.
SELECT
Consultant_ID,
SUM(IIF (Activity = "Working Internally", Datediff("d", maxBegin, minEnd) +1, 0) ) as NonBillable,
SUM(IIF (Activity = "Working Externally", Datediff("d", maxBegin, minEnd) +1, 0) ) as Billable,
SUM(IIF (Activity = "Holidays", Datediff("d", maxBegin, minEnd) +1, 0) ) as Absent
FROM
(
SELECT
*,
(IIF (Beginning_Date > #3/1/2019#, Beginning_Date, #3/1/2019#) ) as maxBegin,
(IIF (End_Date < #3/31/2019#, End_Date, #3/31/2019#) ) as minEnd
FROM Planning
Where Beginning_Date <= #3/31/2019# AND End_Date >= #3/1/2019#
) as z
GROUP BY Planning.Consultant_ID;
Finally, you need to substitute the actual Begin/End dates via params into the sql to run your query. Also note that the Holidays are only 14, not 15.
Also, you can add the Ratio calculation right into this sql, and have only one query.