Can you describe the concept of normalisation?

Normalisation is a process in database design that reduces data redundancy and improves data integrity.

In more detail, normalisation is a systematic approach used in relational database design to ensure that the database is in its most efficient form. It involves organising the columns and tables of a database to minimise data redundancy, which means eliminating duplicate data. This is achieved by ensuring that each piece of data is stored in just one place.

The process of normalisation involves dividing a database into two or more tables and defining relationships between the tables. The main aim of normalisation is to add, delete, or modify a field that can be made in a single table, and then propagated through the rest of the database via the defined relationships.

There are several stages of normalisation, each referred to as a 'normal form.' To be in the first normal form (1NF), a table must have its entries in a specific order, with no duplication of data in any of the rows. The second normal form (2NF) takes this further by ensuring that all non-key attributes are fully functional and dependent on the primary key. The third normal form (3NF) goes even further, requiring that all columns depend directly on the primary key. There are more advanced stages, such as the Boyce-Codd Normal Form (BCNF), fourth normal form (4NF) and fifth normal form (5NF), each with their own specific rules and requirements.

Normalisation has several advantages. It helps to reduce the amount of space a database consumes and ensures that data is logically stored. It also improves the speed and efficiency of most database operations. However, it's worth noting that normalisation should be used judiciously, as over-normalisation can lead to a complex design with many tables, which can slow down data retrieval. Therefore, it's important to strike a balance between normalisation and performance requirements.