Consider the database schema below for cities in countries. A country have many cities, and the same city name can be found in different countries. Country (ID: integer, Name: String (unique)) City...

Consider the database schema below for cities in countries. A country have many cities, and the same city name can be found in different countries.

Country (ID: integer, Name: String (unique))

City (serialNo: integer (unique, not null), CountryID: Integer, CityName: String, Population: integer)

A city can have unknown CityName?