SELECT TOP record for each year

Question

I am trying to recap on my sql skill, now I am trying to run a simple query on northwinddb to show me the top customer for each year, but as soon as I use the TOP function o

Answer 1

Three steps: first sum quantities grouped by company and year, then order the results by quantity, then filter first row by group only.

; WITH sums as (
   SELECT C.Companyname, YEAR(O.OrderDate) AS Year, sum (Quantity) Total
     FROM Customers C JOIN Orders O
    ON C.CustomerID = O.CustomerID JOIN [Order Details] OD
    ON O.OrderID = OD.OrderID
    group by C.Companyname, YEAR(O.OrderDate)
)
with ordering as (
   select Companyname, Year, Total,
          row_number() over (partition by CompanyName, Year order by Total desc) rownum
      from sums
)
select *
from ordering
where rownum = 1