I’ve used the search function quite a bit on this topic but all results seem to differ a bit from what I am trying to achieve….

let’s say I have the following data:

    John          1234       2020/01/01      2020/03/30

I would love to see:
 Name        MemberID   yearnumb   monthnumb  memberall
 John        1234       2020       1          2020/01/01
 John        1234       2020       2          2020/02/01
 John        1234       2020       3          2020/03/01

I'm trying to keep this task in its simplest form and any help would be appreciated as I try and wrap my head around this fairly common procedure!