Use Northwind

--Run  queries on the Customers table 
--Include Execution Plan to view cost
SELECT * FROM customers
SELECT companyname, contactname FROM customers ORDER BY city

SELECT companyname, city FROM customers ORDER BY city

--Create an index to reduce the cost of the above query
DROP INDEX Company ON customers
CREATE UNIQUE NONCLUSTERED INDEX Company
ON customers(city, companyname)

--Run this query again. Is it’s cost reduced? 
SELECT companyname, city FROM customers ORDER BY city