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Normal Forms

The creator of "database normalization," Edgar F. Codd described different "normal forms" a database can adhere to. We'll talk about the most common ones.

First normal form (1NF)
Second normal form (2NF)
Third normal form (3NF)
Boyce-Codd normal form (BCNF)

In short, first normal form is the least normalized form, and Boyce-Codd is the most normalized form we'll cover here.

The more normalized a database, the better its data integrity, and the less duplicate data you'll have.

“Primary Key” in Normal Forms

In the context of database normalization, we're going to use the term "primary key" slightly differently. When we're talking about SQLite, a "primary key" is a single column that uniquely identifies a row.

When we're talking more generally about data normalization, the term "primary key" means the collection of columns that uniquely identify a row. That can be a single column, but it can actually be any number of columns that form a composite key. A primary key is the minimum number of columns needed to uniquely identify a row in a table.

If you think back to the many-to-many joining table product_suppliers, that table's "primary key" was actually a combination of the two IDs, product_id and supplier_id:

CREATE TABLE product_suppliers (
  product_id INTEGER,
  supplier_id INTEGER,
  UNIQUE(product_id, supplier_id)
);