Several design paradigms in the relational database

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1 First normal form (1NF): name, age do not put in the same column (currently it is not possible for anyone to do so)

In any relational database, the first paradigm (1NF) is the basic requirement for relational schemas, and a database that does not meet the first normal form (1NF) is not a relational database.

The so-called First paradigm (1NF) refers to the fact that each column of a database table is an indivisible basic data item and cannot have multiple values in the same column, that is, an attribute in an entity cannot have multiple values or cannot have duplicate properties. If duplicate attributes are present, you may need to define a new entity, which is composed of duplicate attributes, and a one-to-many relationship between the new entity and the original entity. In the first normal form (1NF), each row of a table contains only one instance of information.

In short, the first paradigm is a column with no duplicates.

2 Second Normal form (2NF): There is a self-increment primary key

The second paradigm (2NF) is established on the basis of the first paradigm (1NF), i.e. satisfying the second normal form (2NF) must first satisfy the first paradigm (1NF). The second normal form (2NF) requires that each instance or row in a database table must be divided by a unique region. For the implementation of the distinction, it is common to add a column to the table to store unique identities for each instance. This unique attribute column is called the primary key or primary key, and the main code.

The second normal form (2NF) requires that the attributes of an entity depend entirely on the primary key. A full dependency is a property that cannot exist that relies only on the primary key. If present, then this part of the attribute and primary key should be separated to form a new entity, and the new entity is a one-to-many relationship with the original entity. For the implementation of the distinction, it is common to add a column to the table to store unique identities for each instance.

In short, the second paradigm is that a non-principal attribute is dependent on the primary key.

3 Third normal form (3NF): correlation between tables by primary key

Satisfying the third normal form (3NF) must first satisfy the second normal form (2NF). In short, the third paradigm (3NF) requires that a database table not contain non-primary key information already contained in other tables.

For example, there is a departmental information table, where each department has a department number (dept_id), a department name, a department profile, and so on. Then in the Employee Information table in Figure 3-2, the department number can no longer be the department name, department profile and other departments related information to join the Employee Information table. If there is no departmental information table, it should be built according to the third paradigm (3NF), otherwise there will be a lot of data redundancy.

In short, the third paradigm is that properties do not depend on other non-principal properties.

4 BCNF (BC Paradigm)

5 Paradigm IV (4NF)

6 Paradigm (5NF)

Several design paradigms in the relational database