Working days between dates in an SQL Server Function with flexible options

A flexible and re-usable SQL Server function that will calculate the number of days between two dates with the option to exclude holidays or weekends

Create Holidays Table

If you have checked out the other articles then you may already have the table, if not then use the code below to create it. These are based on standard holidays in England and Wales. On the main page there are functions for other Countries.

SQL

CREATE TABLE Dates.Calendar(CalendarDate DATETIME2 NOT NULL CONSTRAINT PK_CalendarDate PRIMARY KEY,CalendarCA AS (DATEDIFF(DAY,DATEADD(DAY,1-DATEPART(DAY,CalendarDate),CalendarDate),CalendarDate)/7)+1 PERSISTED,CalendarCD AS (DATEDIFF(DAY,CalendarDate,DATEADD(DAY,-1,DATEADD(MONTH,1,DATEADD(DAY,1-DATEPART(DAY,CalendarDate),CalendarDate))))/7)+1 PERSISTED,WeekDayID AS (DATEPART(weekday,[CalendarDate])),WeekDayName AS (case DATEPART(weekday,[CalendarDate]) when (1) then 'Sunday' when (2) then 'Monday' when (3) then 'Tuesday' when (4) then 'Wednesday' when (5) then 'Thursday' when (6) then 'Friday' when (7) then 'Saturday'  end))GODECLARE @D DATETIME2='1850-01-01'WHILE @D<='2099-12-31' BEGININSERT INTO Dates.Calendar(CalendarDate) SELECT @DSET @D=DATEADD(DAY,1,@D)ENDGOCREATE TABLE Dates.CalendarHolidays(CalendarDate DATETIME2 NOT NULL,CalendarFunction INT NOT NULL,HolidayType VARCHAR(100) NULL,CONSTRAINT PK_Holidays_Id PRIMARY KEY(CalendarDate,CalendarFunction))GO/*English & Welsh Holidays*/INSERT INTO Dates.CalendarHolidaysSELECT CalendarDate,0,'New Years Day' FROM Dates.Calendar WHERE DATEPART(MONTH,CalendarDate)=1 AND DATEPART(DAY,CalendarDate)=1 UNION  --New Years DaySELECT CalendarDate,0,'Good Friday' FROM Dates.Calendar WHERE CalendarDate=DATEADD(DAY,-2,Dates.GetEasterDate(DATEPART(YEAR,CalendarDate))) UNION --Good FridaySELECT CalendarDate,0,'Easter Monday' FROM Dates.Calendar WHERE CalendarDate=DATEADD(DAY,1,Dates.GetEasterDate(DATEPART(YEAR,CalendarDate))) UNION --Easter MondaySELECT CalendarDate,0,'May Holidays' FROM Dates.Calendar WHERE DATEPART(MONTH,CalendarDate)=5 AND WeekDayID=2 AND (CalendarCA=1 OR CalendarCD=1)UNION --May HolidaysSELECT CalendarDate,0,'August Holidays' FROM Dates.Calendar WHERE DATEPART(MONTH,CalendarDate)=8 AND WeekDayID=2 AND (CalendarCD=1) UNION --August HolidaysSELECT CalendarDate,0,'Christmas Day' FROM Dates.Calendar WHERE DATEPART(MONTH,CalendarDate)=12 AND DATEPART(DAY,CalendarDate)=25 UNION  --Christmas DaySELECT CalendarDate,0,'Boxing Day' FROM Dates.Calendar WHERE DATEPART(MONTH,CalendarDate)=12 AND DATEPART(DAY,CalendarDate)=26  --Boxing DayGO

Create Function

Now we have the data, we can create a function that loops through each day from the start to the end dates and adds 1 dependent on the variables plugged in as below:

@DateFrom - The starting date for your calculation
@CalendarFunction - The holiday type function you want to use
@DateTo - The end of the date range you want to use
@AdjustMode - Calculate the days between the dates as 0 Exclusive or 1 Inclusive of the first day.
@AdjustWeekend - Excludes weekends from your calculations
@AdjustHolidays - Excludes holidays if the holiday function matches

SQL

CREATE FUNCTION Dates.GetDaysAdjusted(@DateFrom DATETIME2,@CalendarFunction INT,@DateTo AS DATETIME2,@AdjustMode BIT,@AdjustWeekEnds BIT,@AdjustHolidays BIT) RETURNS INT AS BEGIN/*@AdjustMode 0=Count whole days only,1=Any day counts as 1*/IF @DateFrom>@DateTo BEGINDECLARE @T DATETIME2=@DateTo,@F DATETIME2=@DateFromSELECT @DateFrom=@T,@DateTo=@FENDDECLARE @Count AS INT=0,@DateAs DATETIME2=@DateFromWHILE @Date < @DateTo BEGINIF ((DATEPART(WEEKDAY,@Date)IN (1,7)AND @AdjustWeekEnds=1)OREXISTS (SELECT * FROM Dates.CalendarHolidays WHERE CalendarDate=@Date AND CalendarFunction=@CalendarFunctionAND @AdjustHolidays=1))BEGINSELECT @Count = @Count + 1ENDSELECT @Date=DATEADD(DAY,1,@Date)ENDRETURN (DATEDIFF(DAY,@DateFrom,@DateTo)-(@Count))+@AdjustModeENDGOSELECT Dates.GetDaysAdjusted('2014-01-01',0,'2014-01-31',1,1,1)--22SELECT Dates.GetDaysAdjusted('2014-02-01',0,'2014-02-28',1,1,1)--20SELECT Dates.GetDaysAdjusted('2014-05-01',0,'2014-05-02',1,1,1)--2SELECT Dates.GetDaysAdjusted('2014-05-01',0,'2014-05-05',1,1,1)--2SELECT Dates.GetDaysAdjusted('2014-05-01',0,'2014-05-06',1,1,1)--3