Add Column with percentage change in Table Chart

[#1]

Hey,

I have the following problem.

I have a table with 3 columns in my QVD-file.

The colums are month_year, person, sales

month_year	person	sales
201408	A	55
201409	A	66
201408	B	100
201409	B	125
201408	C	5
201409	C	7

I want to solve the following problem:

I want to know how much more ore less a person sales, compared by the last month and the month before the last month, regarding the actual month (201410 in this case)

If I generate an expression as follows:

=(if(Month(month_year)=Month(Today())-1,sales))/(if(Month(month_year)=Month(Today())-2,sales))-1

with the dimension person I only get NULL-values.

Can you help me solving this case?

Thanks a lot in advance and best Regards!

Alexander

[alexandros17]

Could you please mark my answer if you desire ....