Running Sales by Category :Rank Products by Sales Volume and Calculate Running Totals Within Each Category Advanced

          with productsales as
  (select p.category,
          p.name as productname,
          sum(od.quantity) as totalsales
   from orderdetails od
   join products p on od.productid = p.productid
   join suppliers s on p.supplierid = s.supplierid
   group by p.category,
            p.name)
select category,
       productname,
       totalsales,
       rank() over (partition by category
                    order by totalsales desc) as salesrank,
                   sum(totalsales) over (partition by category
                                         order by totalsales desc rows between unbounded preceding and current row) as runningsales
from productsales;