Calculating days to excluding weekends (Monday to Friday) in SQL Server

Question

How can I calculate the number of work days between two dates from table (from the 1st row to the end) in SQL Server 2008?

I tried something like this, but it does

Answer 1

I would always recommend a Calendar table, then you can simply use:

SELECT  COUNT(*)
FROM    dbo.CalendarTable
WHERE   IsWorkingDay = 1
AND     [Date] > @StartDate
AND     [Date] <= @EndDate;

Since SQL has no knowledge of national holidays for example the number of weekdays between two dates does not always represent the number of working days. This is why a calendar table is a must for most databases. They do not take a lot of memory and simplify a lot of queries.

But if this is not an option then you can generate a table of dates relatively easily on the fly and use this

SET DATEFIRST 1;
DECLARE @StartDate DATETIME = '20131103', 
        @EndDate DATETIME = '20131104';

-- GENERATE A LIST OF ALL DATES BETWEEN THE START DATE AND THE END DATE
WITH AllDates AS
(   SELECT  TOP (DATEDIFF(DAY, @StartDate, @EndDate))
            D = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY a.Object_ID), @StartDate)
    FROM    sys.all_objects a
            CROSS JOIN sys.all_objects b
)
SELECT  WeekDays = COUNT(*)
FROM    AllDates
WHERE   DATEPART(WEEKDAY, D) NOT IN (6, 7);

---

EDIT

If you need to calculate the difference between two date columns you can still use your calendar table as so:

SELECT  t.ID,
        t.Date1,
        t.Date2,
        WorkingDays = COUNT(c.DateKey)
FROM    TestTable t
        LEFT JOIN dbo.Calendar c
            ON c.DateKey >= t.Date1
            AND c.DateKey < t.Date2
            AND c.IsWorkingDay = 1
GROUP BY t.ID, t.Date1, t.Date2;

Example on SQL-Fiddle