MySQL -- standardize database design

1、 Why design a database

• When the database is complex , We need to design
• Bad database design ：
  1. data redundancy , Waste space
  2. Database insertion and deletion are troublesome （ Shielding uses physical foreign keys ）
  3. The performance of the program is poor
• Good database design ：
  1. Save a space
  2. Ensure the completion of the database
  3. It is convenient to develop the system
• Database design ：
  1. Analyze requirements ： Analyze the needs of business and demand processing at the moment
  2. Outline design ： Design diagrams E-R chart

2、 Three paradigms

Why data normalization is needed

• Repetition of information
• Update exception
• Insertion exception ： Unable to display information properly
• Delete exception ： Loss of valid information

2.1、 First normal form （1NF）

• Atomicity ： Ensure that a column cannot be further divided

2.2、 Second normal form （2NF）

• Premise ： Satisfy the first paradigm
• Each table only describes one thing

2.3、 Third normal form （3NF）

• Premise ： Satisfy the first paradigm and the second paradigm
• The third paradigm needs to ensure that no column of data in the data table is directly related to the primary key , Not indirectly .

3、 Normative and performance issues

• The associated query cannot have more than three tables
• Consider the needs and goals of commercialization ： Database performance is more important
• When it comes to regulating performance , It needs proper consideration Normative
• Deliberately add some redundant fields to some tables .（ From multi table query to single table query ）
• Intentionally add some calculation Columns （ Reduce the amount of big data to the query of small data , Indexes ）