How to write a GROUP BY SQL query

I have a "Revenue" table which stores the revenue for a Company State combination.

Company int
State   char(2)
IsBiggestState bit
TotalRevenue numeric (10,2)

I need to set the IsBiggestState bit to 1 if the TotalRevenue Amount is the largest amount of all the States within a Company.

How can I write the SQL? Since I am dealing with millions of records, efficiency is of concern.

We are on SQL200开发者_如何学JAVA8 R2.

UPDATE A 
SET A.IsBiggestState = 1
FROM YourTable A
INNER JOIN (SELECT Company, MAX(TotalRevenue) MaxRevenue FROM YourTable
            GROUP BY Company) B
ON A.Company = B.Company AND A.TotalRevenue = B.MaxRevenue

This would address the problem of 2 states having the same TotalRevenue (if that is indeed a problem). It would mark only one of them as the IsBiggestState. I am not entirely sure how the performance compares to other solutions.

UPDATE A 
SET A.IsBiggestState = 1
FROM Revenue A
INNER JOIN 
(
    SELECT
        Company
        ,[State]
        ,ROW_NUMBER() OVER (PARTITION BY Company ORDER BY TotalRevenue desc) as rownum
    FROM Revenue 
) B
ON A.Company = B.Company AND A.[State] = B.[State] AND B.rownum = 1