根据当前时间点的部门对员工历史表进行不同计数

Question

So I have an employee table with data on all employee since the beginning. In the data I have all the data I should need. I have the employee startdate, enddate (null if nothing), I have the name of the department, and if a department has changed, that specific employee has a new line, with a new department value, and two columns called "DepValidFrom" and "DepValidto", in date format that determines the time-period that the current employee was in that specific department.

My goal is, to get into a matrix, a list of all the departments as rows, and with year and month as columns, and the number of employees in that department at that time as values. I have all the data, I just cannot find the exact way to write my PowerBI Measure or perhaps even SQL query.

So.... I am trying to pull this into Power BI, and I am getting an incomplete view. I want my data to look like the following:

Department | Jan | Feb | Mar | Apr |
Dep1       |  3  |  5  |  6  |  4  |
Dep2       |  2  |  3  |  2  |  3  |
Dep3       |  1  |  1  |  2  |  3  |

Right now I am just using a very simple DISTINCTCOUNT(Emp_Table[EmployeeInitials]) which gives me an incomplete view, as it only counts on the specific date, and doesn't retain the number into a total, leaving a bunch of empty values.

I hope someone can understand what I mean, and that someone can help!

Thanks!

Answer 1

You can start by unpivoting the dates and generating a query that gives the number of employee per department and date:

select e.dept, x.dt, sum(cnt) over(partition by dept order by dt) cnt
from employees e
cross apply (values (startdate, 1), (enddate, -1)) as x(dt, cnt)
where dt is not null

Then, you can do conditional aggregation to pivot the results - this requires enumerating the dates though:

select dept, 
    max(case when dt >= '20200101' and dt < '20200201' then cnt else 0 end) cnt_202001,
    max(case when dt >= '20200201' and dt < '20200301' then cnt else 0 end) cnt_202002,
    ...
from (
    select e.dept, x.dt, sum(cnt) over(partition by dept order by dt) cnt
    from employees e
    cross apply (values (startdate, 1), (enddate, -1)) as x(dt, cnt)
    where dt is not null
) t
group by dept

When an employee changes in the middle of the month, it is counted in both departments for that month.