BEx challenge - previous period

Hi,

I have the below BEx query,

"Fiscal period" "Cumulative Balance"

01.2017 10

02.2017 20

03.2017 40

Now i need to have as below

"Fiscal period" "Cumulative Balance(Previous Month)" "Cumulative Balance" "Difference"

01.2017 10 10

02.2017 10 20 10

03.2017 20 40 20

For every "fiscal period" i need to have the previous fiscal period and also i need to calculate the difference between them.

So any way we can achieve this?