Calculate Date by number of working days from a certain Startdate - sql-server-2008

Question

I've got two tables, a project table and a calendar table. The first containts a startdate and days required. The calendar table contains the usual date information, like date, dayofweek, and a column is workingday, which shows if the day is a saturday, sunday, or bank holiday (value = 0) or a regular workday (value = 1).
For a certain report I need write a stored procedure that calculates the predicted enddate by adding the number of estimated workddays needed.
Example:
**Projects**
Name Start_Planned Work_days_Required
Project A 02.05.2016 6
Calendar (04.05 is a bank holdiday)
Day Weekday Workingday
01.05.2016 7 0
02.05.2016 1 1
03.05.2016 2 1
04.05.2016 3 0
05.05.2016 4 1
06.05.2016 5 1
07.05.2016 6 0
08.05.2016 7 0
09.05.2016 1 1
10.05.2016 2 1
Let's say, the estimated number of days required is given as 6 (which leads to the predicted enddate of 10.05.2016). Is it possible to join the tables in a way, which allows me to put something like
select date as enddate_predicted
from calendar
join projects
where number_of_days = 6
I would post some more code, but I'm quite stuck on how where to start.
Thanks!

Answer 1

You could get all working days after your first date, then apply ROW_NUMBER() to get the number of days for each date:
SELECT Date, DayNum = ROW_NUMBER() OVER(ORDER BY Date)
FROM Calendar
WHERE IsWorkingDay = 1
AND Date >= #StartPlanned
Then it would just be a case of filtering for the 6th day:
DECLARE #StartPlanned DATE = '20160502',
#Days INT = 6;
SELECT Date
FROM ( SELECT Date, DayNum = ROW_NUMBER() OVER(ORDER BY Date)
FROM Calendar
WHERE WorkingDay = 1
AND Date >= #StartPlanned
) AS c
WHERE c.DayNum = #Days;
It's not part of the question, but for future proofing this is easier to acheive in SQL Server 2012+ with OFFSET/FETCH
DECLARE #StartPlanned DATE = '20160502',
#Days INT = 6;
SELECT Date
FROM dbo.Calendar
WHERE Date >= #StartPlanned
AND WorkingDay = 1
ORDER BY Date
OFFSET (#Days - 1) ROWS FETCH NEXT 1 ROWS ONLY
ADDENDUM
I missed the part earlier about having another table, and the comment about putting it into a cursor has prompted me to amend my answer. I would add a new column to your calendar table called WorkingDayRank:
ALTER TABLE dbo.Calendar ADD WorkingDayRank INT NULL;
GO
UPDATE c
SET WorkingDayRank = wdr
FROM ( SELECT Date, wdr = ROW_NUMBER() OVER(ORDER BY Date)
FROM dbo.Calendar
WHERE WorkingDay = 1
) AS c;
This can be done on the fly, but you will get better performance with it stored as a value, then your query becomes:
SELECT p.Name,
p.Start_Planned,
p.Work_days_Required,
EndDate = c2.Date
FROM Projects AS P
INNER JOIN dbo.Calendar AS c1
ON c1.Date = p.Start_Planned
INNER JOIN dbo.Calendar AS c2
ON c2.WorkingDayRank = c1.WorkingDayRank + p.Work_days_Required - 1;
This simply gets the working day rank of your start date, and finds the number of days ahead specified by the project by joining on WorkingDayRank (-1 because you want the end date inclusive of the range)
This will fail, if you ever plan to start your project on a non working day though, so a more robust solution might be:
SELECT p.Name,
p.Start_Planned,
p.Work_days_Required,
EndDate = c2.Date
FROM Projects AS P
CROSS APPLY
( SELECT TOP 1 c1.Date, c1.WorkingDayRank
FROM dbo.Calendar AS c1
WHERE c1.Date >= p.Start_Planned
AND c1.WorkingDay = 1
ORDER BY c1.Date
) AS c1
INNER JOIN dbo.Calendar AS c2
ON c2.WorkingDayRank = c1.WorkingDayRank + p.Work_days_Required - 1;
This uses CROSS APPLY to get the next working day on or after your project start date, then applies the same join as before.

Answer 2

This query returns a table with a predicted enddate for each project
select name,min(day) as predicted_enddate from (
select c.day,p.name from dbo.Calendar c
join dbo.Calendar c2 on c.day>=c2.day
join dbo.Projects p on p.start_planned<=c.day and p.start_planned<=c2.day
group by c.day,p.work_days_required,p.name
having sum(c2.workingday)=p.work_days_required
) a
group by name

Answer 3

--This gives me info about all projects
select p.projectname,p.Start_Planned ,c.date,
from calendar c
join
projects o
on c.date=dateadd(days,p.Work_days_Required,p.Start_Planned)
and c.isworkingday=1
now you can use CTE like below or wrap this in a procedure
;with cte
as
(
Select
p.projectnam
p.Start_Planned ,
c.date,datediff(days,p.Start_Planned,c.date) as nooffdays
from calendar c
join
projects o
on c.date=dateadd(days,p.Work_days_Required,p.Start_Planned)
and c.isworkingday=1
)
select * from cte where nooffdays=6

Answer 4

use below logic
CREATE TABLE #proj(Name varchar(50),Start_Planned date,
Work_days_Required int)
insert into #proj
values('Project A','02.05.2016',6)
CReATE TABLE #Calendar(Day date,Weekday int,Workingday bit)
insert into #Calendar
values('01.05.2016',7,0),
('02.05.2016',1,1),
('03.05.2016',2,1),
('04.05.2016',3,0),
('05.05.2016',4,1),
('06.05.2016',5,1),
('07.05.2016',6,0),
('08.05.2016',7,0),
('09.05.2016',1,1),
('10.05.2016',2,1)
DECLARE #req_day int = 3
DECLARE #date date = '02.05.2016'
--SELECT #req_day = Work_days_Required FROM #proj where Start_Planned = #date
select *,row_number() over(order by [day] desc) as cnt
from #Calendar
where Workingday = 1
and [Day] > #date
SELECT *
FROM
(
select *,row_number() over(order by [day] desc) as cnt
from #Calendar
where Workingday = 1
and [Day] > #date
)a
where cnt = #req_day