Third Normal Form

Third Normal Form (3NF):

• The table must already follow the rules of Second Normal Form (2NF).
• Every column should depend only on the primary key, not on other non-key columns.
• If a column depends on another non-key column, move it to a separate table.

Sometimes, you may want to add a new attribute to a table. However, this can significantly increase the table’s size, especially if the attribute is not related to the primary key. In such cases, adding it is not a logical design choice. Consider this example:

In this case, Designer Grade and Designer Country are not true attributes of the Project, they belong to the Designer instead. As in the previous example, if we delete the first row, we would lose important information about Robert Jarry’s grade and country, which indicates poor table design. It’s time to normalize!

Great! You now have separate tables for each entity: the Project table contains only project-related attributes, while the Designer table stores attributes specific to the designer.