First Contact by Category :Find Each Customer’s Earliest Purchase in Every Product Category Intermediate

          with categorizedorders as
  (select o.customerid,
          p.category,
          o.orderid,
          o.orderdate,
          row_number() over (partition by o.customerid,
                                          p.category
                             order by o.orderdate) as orderrank
   from orders o
   join orderdetails od on o.orderid = od.orderid
   join products p on od.productid = p.productid)
select customerid,
       category,
       orderid,
       orderdate
from categorizedorders
where orderrank = 1;