Select dates of a day between two dates.

Introduction

To list out dates of particular day between two days is needed when we are developing any application which having weekly status functinalities. So listing dates of partiuclar day is very help ful in such situtation. fnGetDatesforAday Function gives dates for a day between two dates.

Background

Once I need to list all Sundays betweeen two dates so that time I wrote the code for the same. Later I converted that code to generalize for all days the result is this function.

This function recieves three parameter DateFrom, DateTo and DayName.

• DateFrom : Date from which we want the dates of a day. It accepts date in two formats “MM/DD/YYY” and “MM-DD-YYYY”.

• DateTo : Date upto which we want the dates of a day. It accepts date in two formats “MM/DD/YYY” and “MM-DD-YYYY”.

• DayName: Day name for which we need to list dates. Valid values are “Sunday”, “Monday”, ”Tuesday”, ”Wednesday”, “Thursday”, ”Friday” and ”Saturday”.

This function uses two system function

• DATEDIFF
• DATENAME

The Logic here is first find out the number of days between two dates using DATEDIFF function which returns number of days. So using this number we can loop through each day and check for the required day in the days between start date to end date.

To get day name we use DATENAME function which gives us the day names like “Sunday”, “Monday”, “Tuesday”, “Wednesday”, “Thursday”, “Friday” and “Saturday”, so compare the given day with these days If found insert the date into the table. So finally the table contains all required days dates in the table. Finally return all the dates which are inserted in the table.

Using the code

You can use this code in the select statement or in the stored procedure where you need a date list for the particular day.

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:        Shivshanker cheral
-- Create date: <date month="7" day="18" year="2008" />18 July 2008
-- Description:   To Get any weekday dates between two dates 
-- =============================================

CREATE FUNCTION fnGetDatesforAday
(
      -- Add the parameters for the function here
      @DtFrom DATETIME,
      @DtTo DATETIME,
      @DayName VARCHAR(12)
)

RETURNS @DateList TABLE ([Day] varchar(20),Dt datetime)

AS
BEGIN
      IF NOT (@DayName = 'Monday' OR @DayName = 'Sunday' OR @DayName = 'Tuesday' OR @DayName = 'Wednesday' OR @DayName = 'Thursday' OR @DayName = 'Friday' OR @DayName = 'Saturday')
      BEGIN
            --Error Insert the error message and return

            INSERT INTO @DateList
            SELECT 'Invalid Day',NULL AS DAT
            RETURN
      END 

      DECLARE @TotDays INT
      DECLARE @CNT INT

      SET @TotDays =  DATEDIFF(DD,@DTFROM,@DTTO)-- [NO OF DAYS between two dates]

      SET @CNT = 0
      WHILE @TotDays >= @CNT        -- repeat for all days 
      BEGIN
        -- Pick each single day and check for the day needed
            IF DATENAME(DW, (@DTTO - @CNT)) = @DAYNAME
            BEGIN
                  INSERT INTO @DateList
                 SELECT @DAYNAME,(@DTTO - @CNT) AS DAT
            END
            SET @CNT = @CNT + 1
      END
      RETURN
END

GO 
      

Output:
 SELECT [Day],[Dt] FROM dbo.fnGetDatesforAday('7/1/2008','8/31/2008','Sunday')
 Day Dt
 -------------------- -----------------------
 Sunday 2008-08-31 00:00:00.000
 Sunday 2008-08-24 00:00:00.000
 Sunday 2008-08-17 00:00:00.000
 Sunday 2008-08-10 00:00:00.000
 Sunday 2008-08-03 00:00:00.000
 Sunday 2008-07-27 00:00:00.000
 Sunday 2008-07-20 00:00:00.000
 Sunday 2008-07-13 00:00:00.000
 Sunday 2008-07-06 00:00:00.000 
(9 row(s) affected)

We can list the dates in sorted order with date in different formats according to our needs using convert function and Order by clause.

SELECT [Day],CONVERT(VARCHAR,[Dt],105) AS [Date] FROM dbo.fnGetDatesforAday('7/1/2008','8/31/2008','Sunday') ORDER BY [Dt]

Day                  Date
-------------------- ------------------------------
Sunday               06-07-2008
Sunday               13-07-2008
Sunday               20-07-2008
Sunday               27-07-2008
Sunday               03-08-2008
Sunday               10-08-2008
Sunday               17-08-2008
Sunday               24-08-2008
Sunday               31-08-2008

(9 row(s) affected)

For error it gives the result as Invalid Day in the Day column and Null in Date column

SELECT [Day],CONVERT(VARCHAR,[Dt],105) AS [Date] FROM dbo.fnGetDatesforAday('7/1/2008','8/31/2008','Sumday') ORDER BY [Dt]

Day                  Date
-------------------- ------------------------------
Invalid Day          NULL

(1 row(s) affected)