To homework, asking me to make a table of a DB, the table corresponds to a branch of a department store, this table must contain the following information:
CREATE TABLE STORE
id_store varchar (50),
name_store varchar (50),
city varchar (50),
country varchar (50),
region varchar (50)
You would never want to create a system where the primary key tries to encode data about other attributes in the row. That is the path to great heartache and much suffering.
INSTRto parse out which country a row is in. That is eminently more difficult to index and for the optimizer to understand than a separate column. It's also much harder to ensure that you don't have 'MEX', 'mex', and 'mx' rows all representing Mexico.