Daily distinct Sales using T-SQL for Different Models

Question

This is my input data from a table in db: enter image description here I want to get below information as output: enter image description here

If you observe the output I need to get distinct serial number count for a model from day 1 to till date. for ex: for day1: count(distinct serialnumber) as sold day2 : count(distinct serialnumber from day1) as sold I did this using cumulative sales but because of some serial numbers has multiple sales on different dates, I'm getting a wrong count. Can anyone please help me with T-SQL query for this request?

Answer 1

You could do this with two levels of aggregation:

select model, sale_date, 
    sum(count(*)) over(partition by model order by sale_date) sale_qty
from (
    select model, serial_number, min(sale_date) sale_date
    from mytable
    group by model, serial_number
) t
group by model, sale_date
order by model, sale_date

With this technique, each serial_number is counted only once, on its first appearance date.