Calculate difference between 2 dates in SQL, excluding weekend days

Question

I would like to build an SQL query which calculates the difference between 2 dates, without counting the week-end days in the result.

Is there any way to format the

Answer 1

I've updated @JOpuckman's function to take into account that different regions don't always have a weekend of Saturday and Sunday. Here's the code in case anyone else needs to apply this globally;

DECLARE @FirstDate DateTime
DECLARE @SecondDate DateTime

SET @FirstDate = '08-20-2012'
SET @SecondDate = '08-24-2012'

DECLARE @range INT;
DECLARE @WeekendDayNameStart VARCHAR(50) 
DECLARE @WeekendDayNameEnd VARCHAR(50)

SET @WeekendDayNameStart = 'FRIDAY'
SET @WeekendDayNameEnd = (
    SELECT CASE @WeekendDayNameStart
        WHEN 'SUNDAY' THEN 'MONDAY'
        WHEN 'MONDAY' THEN 'TUESDAY'
        WHEN 'TUESDAY' THEN 'WEDNESDAY'
        WHEN 'WEDNESDAY' THEN 'THURSDAY'
        WHEN 'THURSDAY' THEN 'FRIDAY'
        WHEN 'FRIDAY' THEN 'SATURDAY'
        WHEN 'SATURDAY' THEN 'SUNDAY'
    END
)

DECLARE @NumWorkDays INT

SET @range = DATEDIFF(DAY, @FirstDate, @SecondDate); 
SET @NumWorkDays = (
SELECT  
@range / 7 * 5 + @range % 7 - ( 
    SELECT COUNT(*)  
    FROM ( 
        SELECT 1 AS d 
        UNION ALL SELECT 2  
        UNION ALL SELECT 3  
        UNION ALL SELECT 4  
        UNION ALL SELECT 5  
        UNION ALL SELECT 6  
        UNION ALL SELECT 7 
        ) weekdays 
    WHERE d <= @range % 7  
    AND DATENAME(WEEKDAY, @SecondDate - d) IN (@WeekendDayNameStart, @WeekendDayNameEnd))
);

-- Calculate whether the current date is a working day
DECLARE @CurDateExtra INT
SET @CurDateExtra = 
(
    CASE DATENAME(WEEKDAY, @SecondDate)
    WHEN @WeekendDayNameStart THEN 0
    WHEN @WeekendDayNameEnd THEN 0
    ELSE 1
    END
)

SET @NumWorkDays = @NumWorkDays + @CurDateExtra
SELECT @NumWorkDays