T-SQL Challenge: Find Days of the Week

My personal goal is to post an article every Monday, Wednesday and Friday.  What I’d like to do is create stubs in my content database with each of those days already set aside.  That way, I can look at the next stub available and simply start writing.

The challenge for today is to create a T-SQL script that will list the days in the month that fall on a Monday, Wednesday or Friday.

If you want to take part in this challenge, stop here, and attempt this on your own.

My Solution

My first attempt at this solution had me setting up a few variables.  @daylist, the string that would hold the output.  @dayOfMonth would hold the date we’re testing.  Basically we’re going to iterate through each day of the month and test it to see if it’s a Monday, Wednesday or Friday.  And I needed one last variable to hold on to the current month being tested.  I used a datetime so I’d be able to do date math on the @searchMonth.

After I set up the variables, I entered the current month I wanted to search, and stored that in @dayOfMonth.  Then I set the @searchMonth to the same.  Next I set up the formatting on the @daylist.  I want the output to begin “yyyy/mm:”   and then enter all the dates that match my criteria.

After that, I simply use a WHERE loop to test every day from the 1st to less than the first day of the next month.  In this loop I check the weekday DATEPART of the date.  A DATEPART returns an integer representation of the day of the week.  Sundays are 1, Mondays are 2, etc.

So I simply test for where the weekday DATEPART is 2,4,or 6 and I’m collecting Monday’s Wednesdays and Fridays!

Here is my first solution:

DECLARE @daylist VARCHAR(255)
DECLARE @dayOfMonth DATETIME
DECLARE @searchMonth DATETIME

SET @dayOfMonth = '1/1/2005'
--set the searchmonth = to the current working month
SET @searchMonth = @dayOfMonth
--set the prefix for the @daylist (yyyy/mm: )
SET @daylist = CONVERT(VARCHAR(4), datepart(YEAR, @dayOfMonth)) + '/' 
	+ CONVERT(VARCHAR(2), datepart(MONTH, @dayOfMonth)) + ': '
--PRINT @daylist	

WHILE @dayOfMonth < DATEADD(month, 1, @searchMonth)
BEGIN
	PRINT @dayOfMonth
	IF (datepart(weekday, @dayofMonth) IN (2,4,6))
	BEGIN
		SET @dayList = @daylist + CONVERT(VARCHAR(2), datepart(day, @dayofMonth)) + ', '
	END

	SET @dayOfMonth = DATEADD(day, 1, @dayofMonth)	
END	
	SELECT @daylist

The only problem is you have to enter the month and year for each month and year you want to search…That’s boring. I want to do this a month at a time. Rather than being bored, I decided to “upgrade” the script to run for a year at a time.

By adding a couple variables, one of which being a table variable, I was able to enter a year, and have this script generate the list of Monday, Wednesday and Fridays for the whole year!

DECLARE @daylist VARCHAR(255)
DECLARE @dayOfMonth DATETIME
DECLARE @searchMonth DATETIME
DECLARE @month INT
DECLARE @year INT
DECLARE @monthList TABLE (daylist VARCHAR(255) )
--choose the year you wish to run
SET @year = 2005

SET @month = 1
WHILE @month < 12  --run for every month
BEGIN
	--build the first day of the month
	SET @dayOfMonth = CONVERT(VARCHAR(2), @month) + '/1/' + CONVERT(VARCHAR(4), @year)
	--set the searchmonth = to the current working month
	SET @searchMonth = @dayOfMonth
	--set the prefix for the @daylist (yyyy/mm: )
	SET @daylist = CONVERT(VARCHAR(4), DATEPART(YEAR, @dayOfMonth)) + '/' 
		+ CONVERT(VARCHAR(2), DATEPART(MONTH, @dayOfMonth)) + ': '
	--PRINT @daylist	
	--for every day in the @searchMonth
	WHILE @dayOfMonth < DATEADD(MONTH, 1, @searchMonth)
	BEGIN
		PRINT @dayOfMonth
		--if the weekday is Monday, Wednesday or Friday, include it in our @daylist
		IF (DATEPART(WEEKDAY, @dayofMonth) IN (2,4,6))
		BEGIN
			SET @dayList = @daylist + CONVERT(VARCHAR(2), DATEPART(DAY, @dayofMonth)) + ', '
		END
		--go to the next day
		SET @dayOfMonth = DATEADD(DAY, 1, @dayofMonth)	
	END	
	--insert the @daylist into our table of @daylists
	INSERT INTO @monthList
	SELECT @daylist
	
	SET @month = @month + 1
END
--See the results
SELECT * FROM @monthList

This is the kind of simple problems I love to solve. State the problem, and create a solution. What do you think? What kinds of simple problems have you had to solve using T-SQL? Share them below!

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