A paradigm is a collection of relational patterns that conform to a certain level.
The relationship in the relational database must meet certain requirements, and the ones that meet different levels of requirements are different paradigms.
There are currently six paradigms in relational databases: First Normal Form (1NF), Second Normal Form (2NF), Third Normal Form (3NF), Boyce-Codd Normal Form (BCNF), Fourth Normal Form (4NF) and Fifth Normal Form (5NF) .
The paradigm that meets the minimum requirements is the first normal form (1NF).
On the basis of the first normal form, the one that further satisfies more requirements is called the second normal form (2NF), and the rest can be deduced by analogy.
Generally speaking, the database only needs to satisfy the third normal form (3NF).
The first paradigm: the primary attribute (primary key) is not empty and does not repeat, and the field cannot be divided (there is a partial dependence of non-primary attributes on the primary attribute).
Second normal form: If the relational model is the first normal form, each non-primary attribute has no partial dependence on the primary key.
Third normal form: If the relational model is the second normal form, there is no transitive and partial dependence of non-primary attributes on the primary key.
BCNF paradigm: all attributes do not pass any candidate keys that depend on the relationship.