MySQL table design

1. The paradigm of the database

First normal form, fields are atomic and cannot be further divided (all relational data satisfies the first normal form)

In the second normal form, a table must have a primary key, that is, each row of data can be uniquely distinguished

In the third normal form, a table cannot contain information about non-key fields in other tables, that is, there cannot be redundant fields in the data table;

In practice, the third normal form is often not satisfied, thinking that reasonable redundant fields can reduce join queries

2. Principles of database design

Do not perform operations in the database;

The operation of the cpu must be moved to the business layer;