14. Uniqueness and Keys

The examples in the video are not made up! There actually are five Springfields in the state of Wisconsin.

Country names are not actually as unique as I said in the video, though. There's only one France, but there are two Congos. That is, as of 2016 there are two countries often called "Congo": the Democratic Republic of the Congo, also known as Congo-Kinshasa and previously known as Zaire; and the Republic of the Congo, also known as Congo-Brazzaville.

A better primary key for countries exists, though: the international community has established standard country codes, unique abbreviations for each country. Congo-Kinshasa has country code CD, while Congo-Brazzaville is CG. These are also their Internet top-level domain names.