Group by Month

[#1]

I do have sales numbers on year,month,salesperson.
I want a pivottable with year,month,salesperson and percentage of sales.

Percentage of sales would be calculated on total sales per YearMonth per sales/total sales per YearMonth

The pivottable will contain more than 1 year.

Can anyone help me with the formula to aggregate this in the right way?

[#2]

aggr(sum(salesmonth),salesperson) / aggr(sum(salesmonth),company)?