Sum for previous month with month as dimension

[johnnyjohn]

Say I have the following table where month is a dimension. Sum data is calculated with Sum(data)

Month	Sum data
01/07/2019	1
01/08/2019	2
01/09/2019	3
01/10/2019	4
01/11/2019	5

How can I calculate the sum for the previous month, i.e.

Month	Sum data	Sum data previous month
01/07/2019	1	-
01/08/2019	2	1
01/09/2019	3	2
01/10/2019	4	3
01/11/2019	5	4

[johnnyjohn]

Hello, thanks for answering. I have tried it, but I am not quite sure how this expands on using Above(). The issue I am having is deeper than my original question. Please see the conversations abovee Thanks!