How to calculate Saturday in between two dates in SQL Server - sql-server

Question

Week ends on Saturday and new week starts on Sunday.
I would like to determine date which will be a Saturday and split dates in SQL Server. Example below:
Start_date - 09/11/2018 - Friday
End_date - 12/11/2018 - Monday
Total number of days = 4
I would like split the days and end results as
Start_date - 09/11/2018 - Friday
Date1 - 10/11/2018 - Saturday
Total number of days = 2
Date2 - 11/11/2018 - Sunday
End_date - 12/11/2018 - Monday
Total number of days = 2
Another example ( start_date and end_date if there are more number of Saturdays e.g. )
start-date - 04/05/2017
end_date - 31/05/2017
Then results should be like below :-
Date1 Date2 no. of days.
------------------------------------
04/05/2017 06/05/2017 3
07/05/2017 13/05/2017 7
14/05/2017 20/05/2017 7
21/05/2017 27/05/2017 7
28/05/2017 31/05/2017 4
Please help.
Thanks & Regards,
VG

Answer 1

If I am not mistaken you are looking for something like this:
DECLARE #StartDate DATE = '2017-05-04'
DECLARE #EndDate DATE = '2017-05-31'
DECLARE #OutputTABLE AS TABLE
(
StartDate DATE NOT NULL,
EndDate DATE NOT NULL
)
DECLARE #NumberOfWeeks INT = DATEDIFF(week, #StartDate, #EndDate)
DECLARE #Counter INT = 0
DECLARE #TempDate DATE = DATEADD(week, #Counter, #StartDate)
WHILE #NumberOfWeeks >= 0
BEGIN
IF #NumberOfWeeks = 0
BEGIN
INSERT INTO #OutputTABLE VALUES (#TempDate, #EndDate);
END
ELSE
BEGIN
INSERT INTO #OutputTABLE VALUES (#TempDate, DATEADD(DAY, -1, DATEADD(week, DATEDIFF(week ,0 , #TempDate) + 1, -1)));
END
SET #TempDate = DATEADD(week, #Counter + 1, DATEADD(day, -1, DATEADD(week, DATEDIFF(week, 0, #StartDate), 0)))
SET #NumberOfWeeks = #NumberOfWeeks - 1
SET #Counter = #Counter + 1
END
SELECT StartDate,
EndDate,
DATEDIFF(day, StartDate, EndDate) + 1 AS NumberOfDays
FROM #OutputTABLE

Answer 2

Here is one way. I couldn't figure out a way with a recursive CTE since you can't aggregate in the recursive part of a recursive CTE.
DECLARE #MinDate DATE = '20170504',
#MaxDate DATE = '20170531'
DECLARE #StartDate datetime, #EndDate datetime
--DATE TABLE... ONE ROW FOR EVERY DAY IN RANGE
IF OBJECT_ID('tempdb..#DateTable') IS NOT NULL DROP TABLE #DateTable
SELECT TOP (DATEDIFF(DAY, #MinDate, #MaxDate) + 1)
Dates = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY a.object_id) - 1, #MinDate)
INTO #DateTable
FROM sys.all_objects a
CROSS JOIN sys.all_objects b
IF OBJECT_ID('tempdb..#Results') IS NOT NULL DROP TABLE #Results
CREATE TABLE #Results (Date1 DATETIME, Date2 DATETIME, NumOfDays INT)
--INSERT FIRST ROW IN CASE IT STARTS ON A DAY OTHER THAN SUNDAY
INSERT INTO #Results
SELECT
MIN(Dates) as Date1
,MIN(CASE WHEN DATEPART(WEEKDAY,Dates) = 7 THEN Dates END) as Date2
,DATEDIFF(DAY,MIN(Dates),MIN(CASE WHEN DATEPART(WEEKDAY,Dates) = 7 THEN Dates END)) + 1 as NoOfDays
FROM #DateTable
SET #StartDate = (SELECT MIN(CASE WHEN DATEPART(WEEKDAY,Dates) = 1 THEN Dates END) FROM #DateTable)
SET #EndDate = (SELECT MAX(CASE WHEN DATEPART(WEEKDAY,Dates) = 1 THEN Dates END) FROM #DateTable)
--INSERT ALL FULL WEEKS
WHILE #StartDate < #EndDate
BEGIN
INSERT INTO #Results
SELECT
MIN(Dates) as Date1
,MIN(CASE WHEN DATEPART(WEEKDAY,Dates) = 7 THEN Dates END) as Date2
,DATEDIFF(DAY,MIN(Dates),MIN(CASE WHEN DATEPART(WEEKDAY,Dates) = 7 THEN Dates END)) + 1 as NoOfDays
FROM #DateTable
WHERE Dates >= #StartDate
SET #StartDate = DATEADD(DAY,7,#StartDate)
END
--INSERT LAST ROW IF IT ISN'T A FULL WEEK
IF (SELECT MAX(Date2) FROM #Results) <> #MaxDate
BEGIN
INSERT INTO #Results
SELECT
MIN(Dates) as Date1
,MAX(Dates) as Date2
,DATEDIFF(DAY,MIN(Dates),MAX(Dates)) + 1 as NoOfDays
FROM #DateTable
WHERE Dates > (SELECT MAX(Date2) FROM #Results)
END
SELECT * FROM #Results
DROP TABLE #Results
DROP TABLE #DateTable
RETURNS
+-------------------------+-------------------------+-----------+
| Date1 | Date2 | NumOfDays |
+-------------------------+-------------------------+-----------+
| 2017-05-04 00:00:00.000 | 2017-05-06 00:00:00.000 | 3 |
| 2017-05-07 00:00:00.000 | 2017-05-13 00:00:00.000 | 7 |
| 2017-05-14 00:00:00.000 | 2017-05-20 00:00:00.000 | 7 |
| 2017-05-21 00:00:00.000 | 2017-05-27 00:00:00.000 | 7 |
| 2017-05-28 00:00:00.000 | 2017-05-31 00:00:00.000 | 4 |
+-------------------------+-------------------------+-----------+

Answer 3

This will compute your Date2 from your Date1
print dateadd(day,-1,dateadd(wk,datepart(wk,'4/5/2017'),'1/1/2017'))