2nd Normal Form Definition
A database is in second normal form if it satisfies the following conditions:
It is in first normal form
All non-key attributes are fully functional dependent on the primary key
In a table, if attribute B is functionally dependent on A, but is not functionally dependent on a proper subset of A, then B is considered fully functional dependent on A. Hence, in a 2NF table, all non-key attributes cannot be dependent on a subset of the primary key. Note that if the primary key is not a composite key, all non-key attributes are always fully functional dependent on the primary key. A table that is in 1st normal form and contains only a single key as the primary key is automatically in 2nd normal form.
2nd Normal Form Example
Consider the following example: