1 First paradigm (1NF)
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.
2 second paradigm (2NF)
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. It is often necessary to add a column to the table to store the unique identity of each instance.
The second normal form (2NF) requires that the attributes of an entity depend entirely on the primary key. The so-called full dependency is the inability to have a property that depends only on the primary key, and if so, this part of the property and the primary key should be separated to form a new entity, and the new entity is a one-to-many relationship with the original entity. It is often necessary to add a column to the table to store the unique identity of each instance. In short, the second paradigm is that a non-principal attribute is dependent on the primary key.
3 Third paradigm (3NF)
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 the department number in the Employee Information table can no longer be added to the employee Information table, such as department name, department profile and other department related information. 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.
A detailed explanation of three major paradigms in SQL
