Three paradigms of database

First normal form (1NF)：

There can only be a primary key and a field with relative meaning , The database can no longer be split , It's atomic

Second normal form (2NF)：

The primary and foreign key tables are separated ,

For example , Employees' words , All the information is about employees , Department's words , All the information is about the Department , When two tables are associated , Each table puts the information it represents , Do not store information in other tables , For example, I put the address of my department in the employee table , This is obviously unreasonable , The primary key table contains information about the primary key table , The foreign key table contains information about the foreign key table , This is the second paradigm , Most of us usually use the second paradigm

Third normal form (3NF):

Each key should be directly dependent on the primary key rather than indirectly ,

For example , Now there is a table called room number table , There is a table called room type table , Now I add a column , It's called the room price column , It is obviously unreasonable to put this price in the room number list , Because prices are differentiated by type , So it should be in the type table

【 Be careful 】 On the basis of the first paradigm, the second paradigm , The third paradigm is satisfied on the basis of the second paradigm , If one of them is not satisfied , It does not satisfy the following paradigm