Paradigm Database

When designing a relational database, follow different specification requirements to design a reasonable relational database. These different specification requirements are called different paradigms, and various paradigms present sub-norms. The higher the paradigm, the less redundant the database.

There are currently six normal forms for relational databases: First Normal Form (1NF), Second Normal Form (2NF), Third Normal Form (3NF), Bath-Corder Normal Form (BCNF), Fourth Normal Form (4NF) and Fifth Normal Form ( 5NF, also known as Perfect Normal Form).

All fields in the first normal form should be atomic, that is, each column of the database table is an indivisible atomic data item, not a non-atomic data item such as a collection, array, record, etc. That is, when an attribute in an entity has multiple values, it must be split into different attributes. Each field value in a table conforming to First Normal Form (1NF) can only be an attribute or part of an attribute of an entity. In short, first normal form is a domain without repetitions.
The second normal form requires that the attributes of an entity depend entirely on the primary key. The so-called complete dependency means that there cannot exist an attribute that only depends on a part of the primary key. If it exists, then this attribute and this part of the primary key should be separated to form a new entity, and the new entity and the original entity are one-to-many. relation. In order to realize the distinction, it is usually necessary to add a column to the table to store the unique identifier of each instance. In short, the second normal form is based on the first normal form, the attributes completely depend on the primary key.
The third normal form is based on 1NF, any non-primary attribute does not depend on other non-primary attributes [eliminate transitive dependencies on the basis of 2NF]