USE Northwind
GO

CREATE TABLE myTable99(City varchar(10),UserID varchar(10))
GO

INSERT INTO myTable99(City,UserId)
SELECT 'San Diego', 1 UNION ALL
SELECT 'San Diego', 2 UNION ALL
SELECT 'San Diego', 3 UNION ALL
SELECT 'San Diego', 4 UNION ALL
SELECT 'San Diego', 5 UNION ALL
SELECT 'New York', 1 UNION ALL
SELECT 'New York', 1 UNION ALL
SELECT 'New York', 1 UNION ALL
SELECT 'New York', 1 UNION ALL
SELECT 'New York', 1 UNION ALL
SELECT 'New York', 2 UNION ALL
SELECT 'New York', 3 UNION ALL
SELECT 'New York', 4 UNION ALL
SELECT 'New York', 5 UNION ALL
SELECT 'New York', 6
GO

SELECT TOP 10 city
FROM
	(
		SELECT city, COUNT(city) AS Rank
		FROM myTable99
		GROUP BY city
	) t
ORDER BY Rank DESC

select top 10 city, count(distinct UserID) as no_of_users 
from myTable99 
group by city 
order by count(distinct UserID) desc
GO

DROP TABLE myTable99
GO