Why Normalise?

Bad design causes big problems

Without normalisation, databases suffer from anomalies:

Insertion anomaly — you can't add data without also adding unrelated data

Update anomaly — changing one fact requires updating many rows

Deletion anomaly — deleting a row accidentally removes other important info

Normalisation is the process of organising a database to reduce these problems.

⚠️ Un-normalised table (BAD)
student_name	subject	teacher_name	teacher_email
Alice	Maths	Mr Smith	smith@school.edu
Bob	Maths	Mr Smith	smith@school.edu
Alice	Science	Ms Jones	jones@school.edu