Reccurence from past 12 months to current month (then storing the data)
I am trying to basically get 12 months of past data and compare that 12 months of data to the current month. After I do that, I need to keep that value.
So, we are currently in September 2021, I need the data dating back from August 2021 - September 2020. Taking that data with the Primary Key of CustomerID, I need to know if from those dates in Aug 2021-Sept 2020, if that CustomerID shows up there, I need to know if it shows up in Sept 2021. If it does, then I will need to count it for September 2021.
The tricky part is then once we are through Sept 2021, we will be in Oct 2021, so from there we need the data dating back from Sept 2021 - Oct 2020, and to compare that past 12 months of data to current month of Oct. Then I need to know which CustomerID's reoccurred in month of Oct from the past 12 months... then storing that data and also keeping the underlying data as well so we can see which ones reoccured.