Don't obtain the cumul value for each end of month

[siem]

Hello, I got a table like this :

MaxDat        VALUE

31/01               1000

28/02                1700

31/03                3000

30/04               4100

31/05                4400

I try to have this :

MaxDat        VALUE_no_cumul

31/01               1000

28/02                700

31/03                1300

30/04               1100

31/05                4400

In my script I recover all maxdate but I have no idea how to do the no cumul value for each mont.

Thanks for reading me

[NiTo]

Hi Siem, 

Is there any other field in the table other than maxdate and Value?

[siem]

I got other champ like " statut" or "information" but it's not important for the post.