Select dates of a day between two dates.

Introduction :
Once, I wnated to list all Sundays betweeen two dates. Later I converted that code to generalize for all days the result was this function in the code sample.

To list out dates of particular day between two days is needed when we are developing any application which having weekly status functionaly. So, listing dates of particular day is very helpful in such situtations. fnGetDatesforAday Function gives dates for a day between two dates.

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.

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:  Shivshanker cheral
-- Create date: 18 July 2008
-- Description: To Get any weekday dates between two dates
-- =============================================
-- to list all sundays
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)