I am looking for help on a solution that I cannot seem to wrap my head around.
We have a table that has rows for clients (includes a client_id) for each year that they are involved in projects over the period 2020 until 2025. The clients that had a project in 2020 are 'baseline', let's say that there are 100. Then in 2021 new clients join (e.g. 20), some will leave (e.g. 5) and some will stay and this repeats itself until 2025. In 2020 my total is 100 and in 2021 the delta is 15. Now I'd like to have a visualisation that shows per year the number of new clients and the number of clients that left (so I leave out the clients that continue, only the specific delta matters).
Create a new column called "Baseline" and set it to "Yes" for all rows that have a year of 2020 and "No" for all other years.
Create a new column called "Delta" and set it to 1 for all new clients that appear in a year and -1 for all clients that leave in a year. Set it to 0 for all other rows.
Create a new table that groups the data by year and calculates the sum of the "Delta" column for each year. This will give you the number of new clients and the number of clients that left for each year.