The simplest explanation of the three main paradigms of database

Relationships in relational databases must meet certain requirements, that is, to meet different paradigms. There are currently six paradigms for relational databases: the first paradigm (1NF), the second Normal (2NF), the third Normal (3NF), the fourth Normal (4NF), the V-Normal (5NF), and the sixth (6NF). The paradigm that satisfies the minimum requirements is the first paradigm (1NF). On the basis of the first paradigm further satisfies more requirements called the second normal form (2NF), and the rest of the paradigms are in the second analogy. In general, the database only needs to meet the third normal form (3NF) on the line.

Many of the data on the paradigm are difficult to understand, here summed up the three paradigms, easy for readers to understand.

1NF: The field is atomic and non-divided ;
2NF: Primary key , non-primary key field dependent primary key . Make sure a table shows only one thing
3NF: Non-primary key fields do not depend on each other . Each column has a direct relationship to the primary key, and there is no dependency on the delivery

First paradigm: Examples that do not conform to the first paradigm:

Table: Field 1, Field 2 (Field 2.1, Field 2.2), Field 3 ...

Second paradigm: Examples that do not conform to the second paradigm:

Table: School Number, course number, name, credit;

This table clearly illustrates two transactions: Student information, course information; Because the non-primary key field must rely on the primary key, here the credit depends on the course number, the name dependence and the student number, so does not conform to the two normal forms.

Third paradigm: Examples that do not conform to the third paradigm:

table: School Number, name, age, school, college contact number, college contact number

Presence Dependent Delivery: (school number) → (school) → (college location, college phone)