juniorDatabases
What is a NULL value in SQL?
Updated Apr 28, 2026
Short answer
NULL represents missing or unknown data, not zero or a space.
Deep explanation
Deep dive into foundational storage. Understanding how data is stored on disk vs memory. Discussion on the relational model proposed by E.F. Codd.
Real-world example
A library system where books (primary key) are linked to authors (foreign key).
Common mistakes
- Confusing NULL with an empty string.
Follow-up questions
- What is 3NF?