Create a weekCount column in SQL Server 2012 - sql

Question

I have this data:
id worked_date
-----------------
1 2013-09-25
2 2013-09-26
3 2013-10-01
4 2013-10-04
5 2013-10-07
I want to add a column called weekCount. The based date is 2013-09-25. So all the data with worked_date from 2013-09-25 to 2013-10-01 will have weekCount as 1 and from 2013-10-02 to 2013-10-8 will have weekCount as 2 and so on. How can that be done?
Thanks.

Answer 1

Here's one way using DATEDIFF:
select id,
worked_date,
1 + (datediff(day, '2013-09-25', worked_date) / 7) weekCount
from yourtable
SQL Fiddle Demo

Answer 2

Perhaps an approach like this will solve your problem.
I compute an in-memory table that contains the week's boundaries along with a monotonically increasing number (BuildWeeks). I then compare my worked_date values to my date boundaries. Based on your comment to #sgeddes, you need the reverse week number so I then use a DENSE_RANK function to calculate the ReverseWeekNumber.
WITH BOT(StartDate) AS
(
SELECT CAST('2013-09-25' AS date)
)
, BuildWeeks (WeekNumber, StartOfWeek, EndOfWeek) AS
(
SELECT
N.number AS WeekNumber
, DateAdd(week, N.number -1, B.StartDate) AS StartOfWeek
, DateAdd(d, -1, DateAdd(week, N.number, B.StartDate)) AS EndOfWeek
FROM
dbo.Numbers AS N
CROSS APPLY
BOT AS B
)
SELECT
M.*
, BW.*
, DENSE_RANK() OVER (ORDER BY BW.WeekNumber DESC) AS ReverseWeekNumber
FROM
dbo.MyTable M
INNER JOIN
BuildWeeks AS BW
ON M.worked_date BETWEEN BW.StartOfWeek ANd BW.EndOfWeek
;
SQLFiddle

Answer 3

If you are looking for a Fiscal Week number, I would use a function that would calculate the week:
CREATE FUNCTION FiscalWeek(#FiscalStartDate datetime, #EvalDate datetime)
RETURNS INT
AS
BEGIN
DECLARE #weekNumber INT = (DATEDIFF(DAY, #FiscalStartDate, #EvalDate) / 7) + 1
RETURN (#weekNumber % 52)
END
GO
If you used a fiscal starting date of '2013-09-25' and an evaluation date of '2014-09-25' you would get a week number of 1.
Using a function gives you a little more flexibility to do whatever you need.

Answer 4

Perhaps not the most elegant way but this works for me to get the top rank number:
WITH CTE AS (
SELECT employee_id, DENSE_RANK() OVER (ORDER BY DATEDIFF(DAY, ''20130925'', worked_date )/7 DESC) AS weekRank
FROM Timesheet
)
SELECT TOP (1) weekRank
FROM CTE
WHERE employee_id=#employee_id
ORDER BY weekRank DESC
This is how I can create weekRank column and pass a parameter dynamically:
WITH rank_cte AS (
SELECT timesheet_id,employee_id, date_worked,
dateadd(week, datediff(day,'20000105',worked_date) / 7, '20000105') AS WeekStart,
dateadd(week, datediff(day,'20000105',worked_date) / 7, '20000105')+6 AS WeekEnd,
DENSE_RANK() OVER (ORDER BY 1 + DATEDIFF(DAY, '20130925', worked_date )/7 DESC) AS weekRank
FROM Timesheet
)
SELECT timesheet_id, worked_date, WeekStart, WeekEnd, weekRank
FROM rank_cte rc
WHERE employee_id=#employee_id
AND weekRank=#weekRank
ORDER BY worked_date DESC
Thanks