Question

I have a table containing date, employeeID(int) , and ShiftWorked (can be night/day/weekend or evening) . There is a row for each employee and date combination

I would like to construct a query that gives me a count of how many people have worked a night shift in the week before and after each date in the roster period.

--------------------------------------------------------------------------
Date (yyyy-MM-dd)     | CountOfNightshifts(for 1 week either side of date)
--------------------------------------------------------------------------

2012-1-1              |  8
2012-1-2              |  12
2012-1-3              |  11
2012-1-4              |  6 
etc                   |  etc

I hope this is clear. I have spent days trying to get this to work but I am not getting anywhere.

For example:

SELECT COUNT(id), [date]
FROM ROSTER
WHERE Shift = night AND [date] BETWEEN DATEADD(D,-7,[date]) AND DATEADD(d,7,[date])
GROUP by [date]
group by [date]

This will give me a list of dates and a count of nights on that particular day – not all night shifts in the 7 days before and after the date.

Answer 1

The following query will return two columns: the reference (roster) date and the number of (distinct) people that have worked on the night sift seven days before to seven days after the reference date.

SELECT tmain.date,
(
    SELECT COUNT(DISTINCT taux.employeeId)
    FROM roster taux
    WHERE taux.shiftWorked = 'night'
      AND taux.date >= DATEADD(DAY, -7, tmain.date)
      AND taux.date <= DATEADD(DAY, 7, tmain.date)
) AS [number_of_distinct_people_with_night_shift]
FROM roster tmain
ORDER BY tmain.date;

Note 1: Usually I prefer joins over sub-queries, but I guess this solution is easier to read.

Note 2: I am assuming the time component of date values are irrelevant and all dates have the same time (i.e. ’00:00:00.00′); if it is not the case, there are more adjustments to be done on the date comparison.