- Unnormalised (UNF)
- A table that has not yet been organised into first normal form — typically because one or more fields hold more than one value at once (a repeating group), such as a comma-separated list of subjects in a single cell.
- First Normal Form (1NF)
- Every field holds a single, atomic value (no repeating groups), and every row is uniquely identifiable by its key.
- Second Normal Form (2NF)
- The table is in 1NF, and every non-key field depends on the whole of the primary key — not just part of it. This only becomes an issue when the primary key is composite (made of more than one attribute); a table with a single-attribute key is automatically in 2NF once it's in 1NF.
- Third Normal Form (3NF)
- The table is in 2NF, and no non-key field depends on another non-key field (no transitive dependency) — every non-key field depends on the primary key, the whole primary key, and nothing but the primary key.
- Partial dependency
- A non-key field depends on only part of a composite primary key, rather than the whole key. Fixed by moving that field into a table keyed on just the part it depends on.
- Transitive dependency
- A non-key field depends on another non-key field, which in turn depends on the key — the field depends on the key only indirectly. Fixed by moving the dependent field into a table of its own.
