Beyond Weekends: Addressing Holidays and Custom Workweeks in Your SQL Workday Count

2024-07-27

Counting Work Days Between Two Dates in SQL

Problem:

Given a start date and an end date, we want to find the number of work days (typically Monday to Friday) between them.

Solutions:

There are two main approaches to this problem in SQL:

Using Date Difference and Day of Week Functions:

This method utilizes built-in functions to calculate the total difference in days and then excludes weekends:

SELECT DATEDIFF(day, @StartDate, @EndDate) - 
       (DATEDIFF(week, @StartDate, @EndDate) -
        DATEDIFF(week, DATEADD(day, 1, @StartDate), DATEADD(day, 1, @EndDate))) -
       CASE WHEN DATEPART(WEEKDAY, @StartDate) IN (1, 7) THEN 1 ELSE 0 END + 1 AS WorkDays;

Explanation:

  • DATEDIFF(day, @StartDate, @EndDate): Calculates the total difference in days between the start and end dates.
  • DATEDIFF(week, DATEADD(day, 1, @StartDate), DATEADD(day, 1, @EndDate)): This adjusts for the case where both start and end days are weekends.
  • CASE WHEN DATEPART(WEEKDAY, @StartDate) IN (1, 7) THEN 1 ELSE 0 END: This accounts for the possibility of the start date being a Saturday or Sunday.

Looping Through Dates (Advanced):

This method iterates through each date between the start and end date, checking if it's a weekday and adding the count:

DECLARE @WorkDays INT = 0,
      @CurrentDate DATE = @StartDate;

WHILE @CurrentDate <= @EndDate
BEGIN
  IF DATEPART(WEEKDAY, @CurrentDate) NOT IN (1, 7)
    SET @WorkDays = @WorkDays + 1;
  SET @CurrentDate = DATEADD(day, 1, @CurrentDate);
END;

SELECT @WorkDays AS WorkDays;
  • This method uses a loop variable @CurrentDate starting at the @StartDate.
  • It checks the day of the week using DATEPART(WEEKDAY, @CurrentDate).
  • If it's a weekday (not Saturday or Sunday), it increments the @WorkDays counter.
  • The loop continues until @CurrentDate is greater than @EndDate.

Related Issues and Solutions:

  • Holidays: If you need to exclude specific holidays, you can join with a table containing holiday dates and filter them out in the calculation.
  • Weekends Definition: Some workweeks might differ from Monday-Friday. You can modify the CASE statement or loop condition to adjust for your specific definition.
  • Date Format: Ensure your dates are formatted consistently and compatible with your SQL implementation.

sql t-sql date



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