What are the main levels of normalization in relational databases?

Main levels of data normalization in relational databases:

1. First Normal Form (1NF) — all table attributes contain only atomic (indivisible) values, with no repeating groups.
2. Second Normal Form (2NF) — the table is in 1NF, and all non-key attributes fully depend on the entire composite key (if the key is composite).
3. Third Normal Form (3NF) — the table is in 2NF, and all non-key attributes depend only on the key, without transitive dependencies.

There are more strict forms (Boyce-Codd Normal Form, 4NF, 5NF), but for most practical purposes, the first three are sufficient.