How can I normalize a table that has a foreign key?

Normalizing a table with a foreign key involves structuring your database to reduce redundancy and improve data integrity. Here's how you can approach it:

1. Understand Normalization Principles:

- Normalization typically involves several forms (1NF, 2NF, 3NF, etc.). The most common are the first three. The goal is to eliminate data redundancy and ensure data dependencies are logical.

2. Identify the Foreign Key:

- A foreign key is a column (or set of columns) in one table that refers to the primary key of another table. It establishes a link between the two tables.

3. First Normal Form (1NF):

- Ensure that each column contains only atomic values (no multi-valued attributes). If you have repeating groups of data, create a separate table for them.

4. Second Normal Form (2NF):

- The table must be in 1NF. Additionally, all non-key attributes must be fully functionally dependent on the entire primary key. If a non-key attribute depends on only part of a composite primary key, move it to a separate table.

5. Third Normal Form (3NF):

- The table must be in 2NF. Also, all non-key attributes must be non-transitively dependent on the primary key. This means that non-key attributes should not depend on other non-key attributes.

6. Example Scenario:

- Let's say you have a table called `Orders` with columns like `OrderID`, `CustomerID`, `CustomerName`, `CustomerAddress`, and `OrderDate`. `CustomerID` is a foreign key referencing a `Customers` table.

7. Normalization Steps:

- 1NF: The `Orders` table is already in 1NF if each column contains atomic values.

- 2NF: If `CustomerName` and `CustomerAddress` depend only on `CustomerID` and not on `OrderID`, you should move them to the `Customers` table. The `Orders` table should only contain `OrderID`, `CustomerID`, and `OrderDate`.

- 3NF: If there are no transitive dependencies, the tables are in 3NF. For example, if `CustomerAddress` depends on `CustomerCity`, you might consider creating a separate `Cities` table.

8. Resulting Tables:

- `Customers` table: `CustomerID` (Primary Key), `CustomerName`, `CustomerAddress`.

- `Orders` table: `OrderID` (Primary Key), `CustomerID` (Foreign Key), `OrderDate`.

9. Benefits of Normalization:

- Reduced data redundancy, improved data integrity, easier data maintenance, and more efficient querying.

By following these steps, you can effectively normalize a table that has a foreign key, leading to a more robust and efficient database design.

Learn more about this