Primary and foreign keys: The backbone of relational databases We spoke about normalization but never fully covered primary and foreign keys. It’s not something that’s unique to MySQL, but it’s something that you hear quite frequently: primary key and foreign key. We have already looked at an example of this in the previous MySQL article, but I wanted to elaborate on it a little further. What is a Primary Key in SQL? It’s just a column or combination of columns inside of your table that is unique for each of the entries within that table. A quick example is