How to get date of a beginning of first work weekday even if the Monday is from last month? - sql

Question

My goal to is get get query that will return weekdays in a month. I can get the days of the month but I need to get dates starting from monday through Friday even if the Monday may be in the preceding month.
Example April 1st is a wednesday so I would need to bring back March 30th and 31st. And the last date returned would be by May 1st as that is the last friday that contains some April days..

Answer 1

If interested in a helper function, I have TVF which generates a calendar.
Example
Select * from [dbo].[tvf-Date-Calendar-Wide]('2020-04-01')
Returns
So, with a little tweak, we get can
Select WeekNr = RowNr
,B.*
From [dbo].[tvf-Date-Calendar-Wide]('2020-04-01') A
Cross Apply ( values (Mon)
,(Tue)
,(Wed)
,(Thu)
,(Fri)
) B(Date)
Which Returns
WeekNr Date
1 2020-03-30
1 2020-03-31
1 2020-04-01
1 2020-04-02
1 2020-04-03
2 2020-04-06
2 2020-04-07
2 2020-04-08
...
5 2020-04-29
5 2020-04-30
5 2020-05-01
The Function If Interested
CREATE FUNCTION [dbo].[tvf-Date-Calendar-Wide] (#Date1 Date)
Returns Table
Return (
Select RowNr,[Sun],[Mon],[Tue],[Wed],[Thu],[Fri],[Sat]
From (
Select D
,DOW=left(datename(WEEKDAY,d),3)
,RowNr = sum(Flg) over (order by D)
From (
Select D,Flg=case when datename(WEEKDAY,d)= 'Sunday' then 1 else 0 end
From (Select Top (42) D=DateAdd(DAY,-7+Row_Number() Over (Order By (Select Null)),#Date1) From master..spt_values n1 ) A
) A
) src
Pivot (max(d) for DOW in ([Sun],[Mon],[Tue],[Wed],[Thu],[Fri],[Sat]) )pvg
Where [Sun] is not null
and [Sat] is not null
)
-- Select * from [dbo].[tvf-Date-Calendar-Wide]('2020-04-01')

Answer 2

You first need to find the start of the week for the first day of the month, then the date for the end of the week that contains the last day of the month:
e.g.
SELECT WeekStart = DATEADD(DAY, -(DATEPART(WEEKDAY, '20200401')-1), '20200401'),
WeekEnd = DATEADD(DAY, 7-(DATEPART(WEEKDAY, '20200430')), '20200430');
Gives:
WeekStart WeekEnd
------------------------------
2020-03-29 2020-05-02
You wouldn't want to hard code the first and the last of the month, but these are fairly trivial things to get from a date:
DECLARE #Date DATE = '20200415';
SELECT MonthStart = DATEADD(MONTH, DATEDIFF(MONTH, 0, #Date), 0),
MonthEnd = EOMONTH(#Date);
Which returns
MonthStart MonthEnd
------------------------------
2020-04-01 2020-04-30
You can then just substitute this into the first query for week starts:
DECLARE #Date DATE = '20200401';
SELECT WeekStart = DATEADD(DAY, -(DATEPART(WEEKDAY, DATEADD(MONTH, DATEDIFF(MONTH, 0, #Date), 0))-1), DATEADD(MONTH, DATEDIFF(MONTH, 0, #Date), 0)),
WeekEnd = DATEADD(DAY, 7-(DATEPART(WEEKDAY, EOMONTH(#Date))), EOMONTH(#Date));
Which gives the same output as the first query with hard coded dates. This is very clunky though, so I would separate this out into a further step:
DECLARE #Date DATE = '20200401';
-- SET DATE TO THE FIRST OF THE MONTH IN CASE IT IS NOT ALREADY
SET #Date = DATEADD(MONTH, DATEDIFF(MONTH, 0, #Date), 0);
SELECT WeekStart = DATEADD(DAY, -(DATEPART(WEEKDAY, #Date)-1), #Date),
Weekend = DATEADD(DAY, 7-(DATEPART(WEEKDAY, EOMONTH(#Date))), EOMONTH(#Date));
Again, this gives the same output (2020-03-29 & 2020-05-02).
The next step is to fill in all the dates between that are weekdays. If you have a calendar table this is very simple
DECLARE #Date DATE = '20200415';
-- SET DATE TO THE FIRST OF THE MONTH IN CASE IT IS NOT ALREADY
SET #Date = DATEADD(MONTH, DATEDIFF(MONTH, 0, #Date), 0);
DECLARE #Start DATE = DATEADD(DAY, -(DATEPART(WEEKDAY, #Date)-1), #Date),
#End DATE = DATEADD(DAY, 7-(DATEPART(WEEKDAY, EOMONTH(#Date))), EOMONTH(#Date));
SELECT [Date], DayName = DATENAME(WEEKDAY, [Date])
FROM Calendar
WHERE Date >= #Start
AND Date <= #End
AND IsWeekday = 1
ORDER BY [Date];
If you don't have a calendar table, then I suggest you create one, but if you can't create one you can still generate this on the fly, by generating a set series numbers and adding these numbers to your start date:
DECLARE #Date DATE = '20200415';
-- SET DATE TO THE FIRST OF THE MONTH IN CASE IT IS NOT ALREADY
SET #Date = DATEADD(MONTH, DATEDIFF(MONTH, 0, #Date), 0);
DECLARE #Start DATE = DATEADD(DAY, -(DATEPART(WEEKDAY, #Date)-1), #Date),
#End DATE = DATEADD(DAY, 7-(DATEPART(WEEKDAY, EOMONTH(#Date))), EOMONTH(#Date));
-- GET NUMBERS FROM 0 - 50
WITH Dates (Date) AS
( SELECT TOP (DATEDIFF(DAY, #Start, #End))
DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY n1.n) - 1, #Start)
FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n1 (n)
CROSS JOIN (VALUES (1),(1),(1),(1),(1)) n2 (n)
)
SELECT [Date], DayName = DATENAME(WEEKDAY, [Date])
FROM Dates
WHERE ((DATEPART(WEEKDAY, [Date]) + ##DATEFIRST) % 7) NOT IN (0, 1);

Answer 3

Just generate all possible dates -- up to 6 days before the month begins. Take the valid weekdays after the first Monday:
with dates as (
select dateadd(day, -6, convert(date, '2020-04-01')) as dte
union all
select dateadd(day, 1, dte)
from dates
where dte < '2020-04-30'
)
select dte
from (select d.*,
min(case when datename(weekday, dte) = 'Monday' then dte end) over () as first_monday
from dates d
) d
where datename(weekday, dte) not in ('Saturday', 'Sunday') and
dte >= first_monday;

Answer 4

declare #dateVal datetime = GETDATE(); --assign your date here
declare #monthFirstDate datetime = cast(YEAR(#dateVal) as varchar(4)) + '-' + DATENAME(mm, #dateVal) + '-' + cast(01 as varchar(2))
declare #monthLastDate datetime = DAteADD(day, -1, DATEADD(month, 1, cast(YEAR(#dateVal) as varchar(4)) + '-' + DATENAME(mm, #dateVal) + '-' + cast(01 as varchar(2))))
declare #startDate datetime = DATEADD(DAY, 2 - DATEPART(WEEKDAY, #monthFirstDate), CAST(#monthFirstDate AS DATE))
declare #enddate datetime = DATEADD(DAY, 6 - DATEPART(WEEKDAY, #monthLastDate), CAST(#monthLastDate AS DATE))
Select #startDate StartDate, #enddate EndDate
****Result**
--------------------------------------------------------------
StartDate | EndDate
-----------------------------|--------------------------------
2020-03-02 00:00:00.000 | 2020-04-03 00:00:00.000
-----------------------------|---------------------------------**