tsql row number

SELECT 
   ROW_NUMBER() OVER (
 ORDER BY first_name
   ) row_num,
   first_name, 
   last_name, 
   city
FROM 
   sales.customers;

USE AdventureWorks2012;  
GO  
WITH OrderedOrders AS  
(  
    SELECT SalesOrderID, OrderDate,  
    ROW_NUMBER() OVER (ORDER BY OrderDate) AS RowNumber  
    FROM Sales.SalesOrderHeader   
)   
SELECT SalesOrderID, OrderDate, RowNumber    
FROM OrderedOrders   
WHERE RowNumber BETWEEN 50 AND 60;