1NF, 2NF, and 3NF

Most application databases aim for first, second, and third normal form. These are practical rules for organizing data well.

First normal form (1NF) means each column contains a single atomic value, and each row can be identified uniquely. For example, a column like `products = 'Keyboard, Mouse'` breaks 1NF because it stores multiple values in one field.

Second normal form (2NF) builds on 1NF. It means every non-key column must depend on the whole key, not only part of it. This matters most when a table uses a composite key. If an `order_items` table is keyed by `(order_id, product_id)`, then `quantity` depends on the whole key, but `customer_name` depends only on `order_id` and belongs somewhere else.

Third normal form (3NF) builds on 2NF. It means non-key columns should depend only on the key, not on other non-key columns. For example, if a `customers` table stores `zip_code` and `city`, and `city` is always determined by `zip_code`, then `city` depends indirectly on the customer key. That is a sign the design may need another table.

In practice, 3NF gives you a strong default structure:

customers(id, name, email)
products(id, name, price)
orders(id, customer_id, order_date)
order_items(order_id, product_id, quantity)

Each fact lives where it logically belongs, and the keys describe how the tables connect.