Finding the first and last business day for every month sql - sql

Question

I am trying to find the first and last business day for every month since 1986.
Using this, I can find the first day of any given month using, but just that month and it does not take into consideration whether it is a business day or not. To make it easier for now, business day is simply weekdays and does not consider public holiday.
SELECT DATEADD(s,0,DATEADD(mm, DATEDIFF(m,0,getdate()),0))
But I am not able to get the correct business day, so I created a calendar table consisting of all the weekdays and thought that I can extract the min(date) from each month, but I am currently stuck.
Date
---------------
1986-01-01
1986-01-02
1986-01-03
1986-01-06
...and so on
I have tried to get the first day of every month instead, but it does not take into account whether the day is a weekend or not. It just simply give the first day of each month
declare #DatFirst date = '20000101', #DatLast date = getdate();
declare #DatFirstOfFirstMonth date = dateadd(day,1-day(#DatFirst),#DatFirst);
select DatFirstOfMonth = dateadd(month,n,#DatFirstOfFirstMonth)
from (select top (datediff(month,#DatFirstOfFirstMonth,#DatLast)+1)
n=row_number() over (order by (select 1))-1
from (values (1),(1),(1),(1),(1),(1),(1),(1)) a (n)
cross join (values (1),(1),(1),(1),(1),(1),(1),(1)) b (n)
cross join (values (1),(1),(1),(1),(1),(1),(1),(1)) c (n)
cross join (values (1),(1),(1),(1),(1),(1),(1),(1)) d (n)
) x
I am wondering if anyone can perhaps shed some light as to how can I best approach this issue.

Answer 1

If you already have your calendar table with all available dates, then you just need to filter by weekday.
SET DATEFIRST 1 -- 1: Monday, 7: Sunday
SELECT
Year = YEAR(T.Date),
Month = MONTH(T.Date),
FirstBusinessDay = MIN(T.Date),
LastBusinessDay = MAX(T.Date)
FROM
Calendar AS T
WHERE
DATEPART(WEEKDAY, T.Date) BETWEEN 1 AND 5 -- 1: Monday, 5: Friday
GROUP BY
YEAR(T.Date),
MONTH(T.Date)
You should use the query to mark these days on your calendar table, so it's easy to access them afterwards.
This is how you can mix it up with the generation of the calendar table (with recursion).
SET DATEFIRST 1 -- 1: Monday, 7: Sunday
declare
#DatFirst date = '20000101',
#DatLast date = getdate();
;WITH AllDays AS
(
SELECT
Date = #DatFirst
UNION ALL
SELECT
Date = DATEADD(DAY, 1, D.Date)
FROM
AllDays AS D
WHERE
D.Date < #DatLast
),
BusinessLimitsByMonth AS
(
SELECT
Year = YEAR(T.Date),
Month = MONTH(T.Date),
FirstBusinessDay = MIN(T.Date),
LastBusinessDay = MAX(T.Date)
FROM
AllDays AS T
WHERE
DATEPART(WEEKDAY, T.Date) BETWEEN 1 AND 5 -- 1: Monday, 5: Friday
GROUP BY
YEAR(T.Date),
MONTH(T.Date)
)
SELECT
*
FROM
BusinessLimitsByMonth AS B
ORDER BY
B.Year,
B.Month
OPTION
(MAXRECURSION 0) -- 0: Unlimited

Answer 2

If you got already a table with all the weekdays only:
select min(datecol), max(datecol)
from BusinessOnlyCalendar
group by year(datecol), month(datecol)
But you should expand your calendar to include all those calculations you might do on date, like FirstDayOfWeek/Month/Quarter/Year, WeekNumber, etc.
When you got a column in your calendar indicating business day yes/no, it's a simple:
select min(datecol), max(datecol)
from calendar
where businessday = 'y'
group by year(datecol), month(datecol)