MySQL ---- first acquaintance with MySQL

Concept and installation

The database is “ Organize... According to the data structure 、 Warehouse for storing and managing data ”. Is a long-term storage in the computer 、 organized 、 Shareable 、 A collection of large amounts of data under unified management
It is mainly used to solve the shortcomings of file saving data ：

1. File security issues
2. Files are not conducive to data query and management
3. Files are not conducive to storing large amounts of data
4. It's not convenient to control the file in the program

Mainstream databases ：

• SQL Sever： Microsoft products ,.Net Programmer's favorite , Medium and large scale projects .
• Oracle： Oracle products , Suitable for large projects , Complex business logic , Concurrency is generally not as good as MySQL.
• MySQL： The world's most popular database , It belongs to Oracle , Good concurrency , Not suitable for complex business . Mainly used in e-commerce ,SNS, Forum . For the simple SQL The treatment effect is good .
• PostgreSQL : A relational database developed by the computer department of the University of California, Berkeley , Whether it's for private use , commercial , Or for academic research , Free to use , Modify and distribute .
• SQLite： It's a lightweight database , Abide by ACID Database management system based on RDBMS , It's contained in a relatively small C In the library . Its design goal is embedded , And it has been used in many embedded products , It takes up very low resources , In embedded devices , It may take only a few hundred K That's enough memory .
• H2： It's a use. Java Development of embedded database , It itself is just a class library , It can be directly embedded into the application project

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Linux Next MySQL Installation ：centos7 install Mysql 5.7.27, Detailed and complete tutorial

MySQL Use

Connect to server ：mysql -h [ The goal is IP] -P [ port ] -u root -p
among ：

• Not added -h The parameter represents the default local loopback
• Not added -P Parameter indicates the default 3306 port
  

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• start-up mysql：service mysqld start
• stop it mysql：service mysqld stop
• restart mysql：service mysqld restart
• mysql Whether to start ：service mysqld status

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Create database ：create database [ Database name ];
Display all databases ：show databases;

Delete a database ：drop database [ Database name ];
Use a database ：use [ Database name ];
Create database tables ：create table account(id int, nickname varchar(32), gender varchar(2));
Show table status ：desc [ Table name ];

insert data ：insert into account(id, nickname, gender) values (1, 'test', 'male');
View all the contents of the table ：select * from [ Table name ];

understand MySQL

The essence of a database is that it has a client , The network program of the server ,MySQL Is a portable database

Database program understanding ：

• adopt MySQL Client to mysqld server Sponsored create database Create table operation , stay Linux The essence is in /var/lib/mysql Create a directory ,
  
• Create a table structure in a database , Essentially, it is to create multiple ordinary files
  

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MySQL framework ：
Be careful ： All in the application layer

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SQL classification ：

• DDL【data definition language】 Data definition language , Used to maintain the structure of stored data , For instructions : create, drop, alter
• DML【data manipulation language】 Data manipulation language , Used to manipulate data , For instructions ： insert,delete,update
• DML There is another one in the DQL【Data QueryLanguage】, Data query language , For instructions ： select
• DCL【Data Control Language】 Data control language , Mainly responsible for authority management and affairs , For instructions ： grant,revoke,commit

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MySQL Supported storage engines ：
show engines; The most commonly used is InnoDB and MyISAM