The second paradigm (2NF): the relational schema R belongs to first normal form, and each non-main attribute is completely dependent on the key code in function.

The third paradigm (3NF): the relational schema R belongs to first normal form, and each non-main attribute is not bound to the key code.

Second, the content is different:

The second normal form (2NF): firstly, it is 1NF, which contains two parts: one is that the table must have a primary key; Second, columns that are not included in the primary key must depend entirely on the primary key, not just on a part of it.

The Third Paradigm (3NF): First, 2NF. In addition, non-primary key columns must depend directly on the primary key and cannot have transitive dependencies. That is, it cannot exist: non-primary key column A depends on non-primary key column B, and non-primary key column B depends on primary key.

Second normal form

This relationship is usually called functional dependence, that is, other data elements in the table depend on the primary key, or the data elements are uniquely identified by the primary key. The second paradigm is the paradigm used in database normalization. Its rule is that all non-primary attributes in the data table must depend entirely on the primary key of the data table; If any non-primary attribute is only related to a part of the primary key, it does not conform to the second normal form.

Refer to the above content: Baidu Encyclopedia-Second Paradigm