Group By selecting fixed rows returned and ignoring the top row SQL Server

Question

I have a table:

Customer           Purchase
John                 5
John                 8
John                 3
John                 1  
Sally                3
Sally                5
Sally                2

I want to return two records per customer ignoring the top purchase:

John                  5
John                  3
Sally                 3
Sally                 2 

Answer 1

With ROW_NUMBER() window function:

select t.customer, t.purchase
from (
  select *, row_number() over (partition by customer order by purchase desc) rn
  from tablename
) t
where t.rn between 2 and 3