How to calculate difference between two dates in workdays - sql-server

Question

I need to calculate difference in workdays between two dates. Is there a built in function for this in SQL Server? Can someone please provide an example on how to do this?

Answer 1

Here is something I wrote quickly. Just encapsulate it into a function or whatever you need.
declare #StartDate datetime
declare #EndDate datetime
declare #TotalDiff int
declare #NumberOfWeekends int
SET #StartDate = '3/12/2013'
SET #EndDate = '3/22/2013'
SET #NumberOfWeekends = 0
SET #TotalDiff = DATEDIFF(d,#StartDate, #EndDate)
If #TotalDiff > 7
SET #NumberOfWeekends = #TotalDiff / 7
else if DATEPART(dd, #EndDate) < DATEPART(DD, #StartDate)
SET #NumberOfWeekends = 1
select (#TotalDiff - 2*#NumberOfWeekends) as TotalWorkDays

Answer 2

No, there is nothing built in to SQL Server to directly give you number of working days between two dates, however there are a few built-in functions which will enable you to write one.
Firstly, a few caveats
The world cannot agree what a "Working Day" is. For most of us it's Saturday and Sunday. For most of the Middle East it's Friday & Saturday (with Sunday being a normal working day)
The world most certainly cannot agree on what constitutes a public holiday, which are almost always considered non-working days.
You have not specified how you would like to handle these cases so lets make some assumptions:
Saturday and Sunday will be non-working days
Public holidays will not be taken into acount
Now, determining if a particular days is saturday or sunday in sql is easy, given a #date of type DateTime:
IF DATENAME(dw,#date) IN ('Saturday','Sunday')
With that in mind, given a start and end date, you can just count incrementally from #startDate to #endDate
DECLARE #startDate DATETIME = '2013-01-01'
DECLARE #endDate DATETIME = '2013-01-20'
DECLARE #currDate DATETIME = #startDate
DECLARE #numDays INT = 0
WHILE #currDate<#endDate
BEGIN
IF DATENAME(dw,#currDate) NOT IN ('Saturday','Sunday')
SET #numDays = #numDays + 1
SET #currDate = DATEADD(day,1,#currDate)
END
SELECT #numDays
Note: This is non-inclsive so wont count #endDate. You could change it to be inclusive by changing WHILE #currDate<#endDate to WHILE #currDate<=#endDate

Answer 3

My solution does not count the #EndDate, so if you need to change that, just add 1 to #d2.
First, I calculate the number of days from an "initial" day (which happens to be 1/1/1900, a Monday) to #StartDate and #EndDate:
DECLARE #d1 int = DATEDIFF(Day, 0, #StartDate);
DECLARE #d2 int = DATEDIFF(Day, 0, #EndDate);
Then, the total number of days between #StartDate and #EndDate is:
#d2 - #d1
From this, I substract the number of Sundays and the number of Saturdays in the interval, each calculated as a difference simlar to the total days, but now for whole weeks (7 days). To get the number of whole weeks, I use integer division by 7 and the fact that the "initial" day (0) is a Monday. The number of Sundays in the interval is
#d2/7 - #d1/7
and the number of Saturdays is
(#d2+1)/7 - (#d1+1)/7
Putting all together, my solution is:
DECLARE #StartDate DATETIME = '20180101'
DECLARE #EndDate DATETIME = '20180201'
DECLARE #d1 int = DATEDIFF(Day, 0, #StartDate)
DECLARE #d2 int = DATEDIFF(Day, 0, #EndDate)
SELECT #d2 - #d1 - (#d2/7 - #d1/7) - ((#d2+1)/7 - (#d1+1)/7) AS workdays