A brief introduction to database mysql

One 、 Basic concepts of database

1、 The composition of the database

• data （Data）
  • A symbolic record of things
  • Including digital , written words 、 graphics 、 Images 、 voice 、 Records, etc
  • With “ Record ” Forms are stored in a unified format
• surface
  • Organize different records together , Used to store specific data
• database
  • Set of tables , It's a warehouse for storing data
  • A collection of interrelated data stored in a certain organization

2、 Database system

• Database system （DBS）
  • It's a human computer system , By hardware 、OS、 database 、DBMS、 Application software and database users
  • The user can go through DBMS Or the application operates the database

• Database management system （DBMS)
  • Is to achieve effective organization of database resources 、 System software for management and access
  • function ： Establishment and maintenance of database 、 Data definition function 、 Data manipulation function 、 Database operation and management functions 、 Communications functions

Two 、 The history of database system development

1、 First generation database

• since 20 century 60 s , The first generation database system came out
• It is a database system of hierarchical model and mesh model
• It provides strong support for unified management and data sharing

2、 Second generation database

• 20 century 70 s , Second generation database —— Relational databases are beginning to appear
• 20 century 80 s ,IBM The company's relational database system DB2 available , Start to gradually replace the database of hierarchical and mesh model , Become the mainstream of the industry
• up to now , Relational database system still occupies the main position of database application

3、 Third generation database

• since 20 century 80 s , New database systems for different fields are emerging
• Object oriented database system , Practical 、 It has a wide range of adaptability
• 20 century 90 Late S , A variety of database systems support applications together
• Some new elements have been added to mainstream database systems
  • for example ,Oracle Supported by “ Relationship — object ” database model

3、 ... and 、 Today's mainstream databases

• SQL Server ( Microsoft products )
  • oriented Windows operating system
  • Simple 、 Easy to use
• Oracle （ Oracle products ）
  • For all mainstream platforms
  • Security 、 perfect 、 The operation is complicated
• DB2 (IBM The products of the company )
  • For all mainstream platforms
  • large 、 Security 、 perfect
• MySQL （ Oracle buys ）
  • free 、 Open source 、 Small volume
    Most companies use MySQL, Because it's free 、 Open source .

Four 、 Introduction to relational database

1、 Understanding relational databases

• Relational database system is a database system that organizes data based on relational model
• The data structure of relational model uses two-dimensional data table which is easy to understand
  • Each line is called a record , Information used to describe an object
  • Each column is called a field , Used to describe an attribute of an object
• The relational model can be simply " Entity - Relationship "（E-R） It is shown in the figure
• E-R Include entities in the diagram （ Data objects ）、 Three elements of relationship and attribute
  
• Entity
  • Also known as instances , Corresponding to the real world can be distinguished from other objects “ event ” or “ thing ”
  • For example, bank customers 、 Bank accounts, etc
• attribute
  • A property of an entity , An entity can have multiple properties
  • for example “ Bank customers ” Each entity in the entity set has a name 、 address 、 Phone and other attributes
• contact
  • The correspondence between entity sets is called connection , Also called relationship
  • For example, there is a relationship between a bank customer and a bank account “ savings ” The relationship between
• A collection of all entities and relationships between entities form a relational database

2、 Application of relational database

（1） Relational database

• Oracle、Mysql
• SQLServer、Sybase
• Informix、access
• DB2、FoxPRO

（2） Applications in life

• 12306 User information system
• Taobao account system
• Website user information system, etc

5、 ... and 、 Introduction to non relational database

• Non relational databases are also called NoSQL (Not Only SQL)
• Storing data is not based on a relational model , No fixed table format is required
• Advantages of non relational database
  • Database can be read and written with high concurrency
  • Efficient storage and access to massive data
  • Database has high scalability and high availability
• Common non relational databases
  • Redis
  • mongoDB

6、 ... and 、MySQL Database introduction

1、MySQL

• A popular open source relational database
• Oracle Our products
• comply with GPL agreement , It can be used and modified free of charge
• characteristic
  • Performance is remarkable 、 Stable service
  • Open source 、 No copyright restrictions 、 The cost is low
  • Multithreading 、 Multi user
  • be based on C/S（ client / The server ） framework
  • Safe and reliable

2、MySQL Business and community

（1）MySQL Business and community

• MySQL The commercial version is made up of MySQL AB The company is responsible for the development and maintenance of , You need to pay to use
• MySQL The Community Edition is made up of MySQL developer 、 Fans work together to develop and maintain , Free to use

（2） Difference between them

• The organization, management and testing of the commercial version are more strict , It will be more stable than the community version
• The commercial version does not comply with GPL, Community compliance GPL Free to use
• The commercial version is available 7*24 Hours of service , The community edition does not