Count work days between two dates

Question

How can I calculate the number of work days between two dates in SQL Server?

Monday to Friday and it must be T-SQL.

Answer 1

None of the functions above work for the same week or deal with holidays. I wrote this:

create FUNCTION [dbo].[ShiftHolidayToWorkday](@date date)
RETURNS date
AS
BEGIN
    IF DATENAME( dw, @Date ) = 'Saturday'
        SET @Date = DATEADD(day, - 1, @Date)

    ELSE IF DATENAME( dw, @Date ) = 'Sunday'
        SET @Date = DATEADD(day, 1, @Date)

    RETURN @date
END
GO

create FUNCTION [dbo].[GetHoliday](@date date)
RETURNS varchar(50)
AS
BEGIN
    declare @s varchar(50)

    SELECT @s = CASE
        WHEN dbo.ShiftHolidayToWorkday(CONVERT(varchar, [Year]  ) + '-01-01') = @date THEN 'New Year'
        WHEN dbo.ShiftHolidayToWorkday(CONVERT(varchar, [Year]+1) + '-01-01') = @date THEN 'New Year'
        WHEN dbo.ShiftHolidayToWorkday(CONVERT(varchar, [Year]  ) + '-07-04') = @date THEN 'Independence Day'
        WHEN dbo.ShiftHolidayToWorkday(CONVERT(varchar, [Year]  ) + '-12-25') = @date THEN 'Christmas Day'
        --WHEN dbo.ShiftHolidayToWorkday(CONVERT(varchar, [Year]) + '-12-31') = @date THEN 'New Years Eve'
        --WHEN dbo.ShiftHolidayToWorkday(CONVERT(varchar, [Year]) + '-11-11') = @date THEN 'Veteran''s Day'

        WHEN [Month] = 1  AND [DayOfMonth] BETWEEN 15 AND 21 AND [DayName] = 'Monday' THEN 'Martin Luther King Day'
        WHEN [Month] = 5  AND [DayOfMonth] >= 25             AND [DayName] = 'Monday' THEN 'Memorial Day'
        WHEN [Month] = 9  AND [DayOfMonth] <= 7              AND [DayName] = 'Monday' THEN 'Labor Day'
        WHEN [Month] = 11 AND [DayOfMonth] BETWEEN 22 AND 28 AND [DayName] = 'Thursday' THEN 'Thanksgiving Day'
        WHEN [Month] = 11 AND [DayOfMonth] BETWEEN 23 AND 29 AND [DayName] = 'Friday' THEN 'Day After Thanksgiving'
        ELSE NULL END
    FROM (
        SELECT
            [Year] = YEAR(@date),
            [Month] = MONTH(@date),
            [DayOfMonth] = DAY(@date),
            [DayName]   = DATENAME(weekday,@date)
    ) c

    RETURN @s
END
GO

create FUNCTION [dbo].GetHolidays(@year int)
RETURNS TABLE 
AS
RETURN (  
    select dt, dbo.GetHoliday(dt) as Holiday
    from (
        select dateadd(day, number, convert(varchar,@year) + '-01-01') dt
        from master..spt_values 
        where type='p' 
        ) d
    where year(dt) = @year and dbo.GetHoliday(dt) is not null
)

create proc UpdateHolidaysTable
as

if not exists(select TABLE_NAME from INFORMATION_SCHEMA.TABLES where TABLE_NAME = 'Holidays')
    create table Holidays(dt date primary key clustered, Holiday varchar(50))

declare @year int
set @year = 1990

while @year < year(GetDate()) + 20
begin
    insert into Holidays(dt, Holiday)
    select a.dt, a.Holiday
    from dbo.GetHolidays(@year) a
        left join Holidays b on b.dt = a.dt
    where b.dt is null

    set @year = @year + 1
end

create FUNCTION [dbo].[GetWorkDays](@StartDate DATE = NULL, @EndDate DATE = NULL)
RETURNS INT 
AS
BEGIN
    IF @StartDate IS NULL OR @EndDate IS NULL
        RETURN  0

    IF @StartDate >= @EndDate 
        RETURN  0

    DECLARE @Days int
    SET @Days = 0

    IF year(@StartDate) * 100 + datepart(week, @StartDate) = year(@EndDate) * 100 + datepart(week, @EndDate) 
        --same week
        select @Days = (DATEDIFF(dd, @StartDate, @EndDate))
      - (CASE WHEN DATENAME(dw, @StartDate) = 'Sunday' THEN 1 ELSE 0 END)
      - (CASE WHEN DATENAME(dw, @EndDate) = 'Saturday' THEN 1 ELSE 0 END)
      - (select count(*) from Holidays where dt between @StartDate and @EndDate)
    ELSE
        --diff weeks
        select @Days = (DATEDIFF(dd, @StartDate, @EndDate) + 1)
      - (DATEDIFF(wk, @StartDate, @EndDate) * 2)
      - (CASE WHEN DATENAME(dw, @StartDate) = 'Sunday' THEN 1 ELSE 0 END)
      - (CASE WHEN DATENAME(dw, @EndDate) = 'Saturday' THEN 1 ELSE 0 END)
      - (select count(*) from Holidays where dt between @StartDate and @EndDate)
 
    RETURN  @Days
END