Complex auto-increase number based on other column information


#1

Hi Airtable community,

My problem is a bit complex and hope I am putting it simple enough.

I have a project list and a customer list stored in two separated tables. Each project is assigned with one customer. Each project is also assigned with a create-date (sorted in natural order).

I would like to have an index number for each project. So this index number starts to count for each year and each customer.

So something like the last number. The number should be auto increases along the project counts, but only for per year and per customer

Project 1 | Customer A | 2017 | 1
Project 2 | Customer A | 2017 | 2
Project 3 | Customer B | 2017 | 1
Project 4 | Customer B | 2017 | 2
Project 5 | Customer B | 2018 | 1
Project 6 | Customer B | 2018 | 2
Project 7 | Customer B | 2018 | 3
Project 8 | Customer C | 2018 | 1
Project 9 | Customer C | 2018 | 2

This is a legacy coding system used in old admin tasks.

Thanks in advance.

Best Regards

K.