Explain the concept of database normalization in MySQL.

Database normalization is a process used to organize a relational database efficiently, reducing data redundancy and dependency. It involves structuring the database schema in a way that minimizes redundancy and ensures data integrity while also improving query performance. In MySQL, normalization is typically achieved through a series of steps called normal forms.

The most common normal forms are:

  1. First Normal Form (1NF):
    • Eliminate repeating groups: Each field should contain atomic values, meaning no repeating groups or arrays should exist within a single field.
    • Ensure each column has a unique name.
    • Create a separate table for each set of related attributes, and assign a primary key to each table.
  2. Second Normal Form (2NF):
    • Meet the requirements of 1NF.
    • Eliminate partial dependencies: Each non-key attribute must be fully functionally dependent on the primary key.
    • Move attributes that are not fully dependent on the primary key to another table.
  3. Third Normal Form (3NF):
    • Meet the requirements of 2NF.
    • Eliminate transitive dependencies: Non-key attributes should not depend on other non-key attributes.
    • Move non-key attributes that depend on other non-key attributes to another table.

Achieving higher normal forms like Boyce-Codd Normal Form (BCNF) and Fourth Normal Form (4NF) involves further eliminating more complex dependencies, but 3NF is usually considered sufficient for most database designs.

In MySQL, normalization is typically implemented through the creation of multiple tables and establishing relationships between them using foreign keys. Here's an example:

Suppose we have a database for a library with the following tables:

  • books (book_id, title, author_id, ISBN)
  • authors (author_id, author_name, birth_date)

To normalize this schema:

  1. We ensure each table meets 1NF by making sure each column contains atomic values and assigning a unique name to each column.
  2. We can split the books table into two tables to meet 2NF:
    • books (book_id, title, author_id, ISBN)
    • authors (author_id, author_name, birth_date)
  3. To meet 3NF, we ensure there are no transitive dependencies. In this case, we move the non-key attribute author_name from the books table to the authors table.