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

As with DATEDIFF, I do not consider the end date to be part of the interval. The number of (for example) Sundays between @StartDate and @EndDate is the number of Sundays between an "initial" Monday and the @EndDate minus the number of Sundays between this "initial" Monday and the @StartDate. Knowing this, we can calculate the number of workdays as follows:

DECLARE @StartDate DATETIME
DECLARE @EndDate DATETIME
SET @StartDate = '2018/01/01'
SET @EndDate = '2019/01/01'

SELECT DATEDIFF(Day, @StartDate, @EndDate) -- Total Days
  - (DATEDIFF(Day, 0, @EndDate)/7 - DATEDIFF(Day, 0, @StartDate)/7) -- Sundays
  - (DATEDIFF(Day, -1, @EndDate)/7 - DATEDIFF(Day, -1, @StartDate)/7) -- Saturdays

Best regards!