MySQL-09

9、 Standardize database design

9.1、 Why design is needed

When the database is complex , It needs to be designed

Bad database design ：

• data redundancy , Waste space

• Database insertion and deletion are troublesome 、 abnormal [ Shielding uses physical foreign keys ]

• The performance of the program is poor

Good database design ：

• Save memory space
• Ensure the integrity of the database
• It is convenient to develop the system

Software development , About the design of database

• Analyze requirements ： Analyze the business and the database needs to be processed
• Outline design ： Design diagrams E-R chart

The steps to design a database （ Personal blog ）：

• To collect information , Analyze requirements
  • User table （ User login and logout , User's personal information , Blogging , Create classification ）
  • Classification table （ The article classification , Who created ）
  • Article table （ Information about the article ）
  • Comment table
  • Friend list （ Friend chain information ）
  • Custom table （ system information , A key word , Or some main fields ）key:value
  • Tell me about the watch （ Publish your mood … ID … CONTENT … CREATE_TIME）
• Identifying entities （ Implement the requirements to each field ）
• Identify the relationship between entities
  • Blogging ：user- >blog
  • Create classification ：user->category
  • Focus on ：user->user
  • Friend chain ：links
  • Comment on ：user-user-blog

9.2、 Three paradigms

Why design standardization is needed

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

Three paradigms （ understand , Written examination may ask ）

First normal form （1NF）

Atomicity ： Make sure that each column is no longer divisible

Second normal form （2NF）

Premise ： Satisfy the first paradigm

Each table only describes one thing

** Third normal form （3NF） **

Premise ： Satisfy the first paradigm and the second paradigm

The third paradigm needs to ensure that each column of data in the data table is directly related to the primary key , Not indirectly

Standardize the design of database

Normative and performance The problem of

The associated query cannot have more than three tables

• Consider the needs and goals of commercialization ,（ cost , User experience ！） Database performance is more important
• When it comes to regulating performance , We need to give due consideration to normalization
• 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 data from large to small ： Indexes ）