Count number of results per CustomerID

I am looking into phone calls to customers and I need a column that count the results for previous calls to the same customer.

E.g how many of the prior calls has ended with the result “No Contact”

I have been looking into the CASE WHEN function and the LAG function, but I haven’t been able get the result I am looking for

The below and example of what I am trying to achieve (the PriorNotInterested column):

Answer

You want a conditional window sum() between the first record of the client and the record preceeding the current one. Most RDBMS support the rows between clause in window functions:

select 
    t.*,
    sum(case when Result = 'Not Interested' then 1 else 0 end)
        over (
            partition by customer_id 
            order by Call_date
            rows between unbounded preceding and 1 preceding
        ) CountNotIntererstedPrior
from mytable t