How many customers does it have?
SELECT count ( * )  FROM Customers AS T1 JOIN Addresses AS T2 ON T1.customer_address_id  =  T2.address_id GROUP BY T2.city ORDER BY count ( * )  DESC LIMIT 1
counting customers refers to COUNT(*); customers are represented by entries in the Customers table; grouping by city involves grouping entries based on the city from the Addresses table; the highest number of customers in a city refers to ORDER BY COUNT(*) DESC LIMIT 1;