Question

Is it ok if i dont use a foreign key, when i could use it, i just dont use it?

For example, my COUNTRY_STATE table should have Country.Id as the foreign key, but i didn’t do that instead have CountryCode. I get the states for each country by CountryCode.

COUNTRY
-Id (PK)
-Code
-Name

---

COUNTRY_STATE
-Id (PK)
-Code
-Name
-CountryCode 

Answer 1

A foreign key does not necessarily need to reference a primary key. It can also reference a unique constraint.

So if you want to keep the country_code in the country_state table, you can do that and still have a foreign key that ensure that only valid country codes are used:

ALTER TABLE country 
  ADD CONSTRAINT uq_code UNIQUE (code);

ALTER TABLE country_state 
    ADD CONSTRAINT fk_state_country 
    FOREIGN KEY (country_code) REFERENCES country (code);