First knowledge database

Hello everyone , I meet you again , I'm your friend, Quan Jun .

data Library preliminary understanding

What is data (Data)

 The so-called data can be symbols 、 written words 、 Numbers 、 voice 、 Images 、 Video and other specific information    It is used to describe things 

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What is a database (DataBase abbreviation DB)

 Database is a space or warehouse for storing data, but this warehouse is on the computer storage device , And the data is stored in a certain format 

 The data in the database is organized according to a certain data model 、 Describe and store , With less redundancy 、 High data independence and scalability , And can be used for all kinds of   User sharing 

 The database can also be regarded as the file in the folder, which is the table in the database 

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Database classification ：

1. Relational database 2. Non relational database

　　 Relational database ： Tables are related to each other You can create tables ( I.e. documents )

Relational databases have :mysql oracale db2 mariadb etc.

Non-relational databases do : mongodb,redis,memcache

The features and advantages and disadvantages of relational database and non relational database

Database type	characteristic	advantage	shortcoming
Relational database SQLite、Oracle、mysql	1、 Relational database , A database that uses a relational model to organize data ;2、 The biggest characteristic of relational database is the consistency of transaction ;3、 Simply speaking , A relational model is a two-dimensional table model , A relational database is a data organization composed of two-dimensional tables and their relationships .	1、 Easy to understand ： Two dimensional table structure is a concept very close to the logical world , Relational models are relatively mesh 、 Layers and other models are easier to understand ;2、 Easy to use ： General purpose SQL Language makes it very convenient to operate relational database ;3、 Easy to maintain ： Rich integrity ( Entity integrity 、 Referential integrity and user-defined integrity ) It greatly reduces the probability of data redundancy and data inconsistency ;4、 Support SQL, Can be used for complex queries .	1、 In order to maintain consistency, the huge cost is its poor read-write performance ;2、 Fixed watch structure ;3、 High concurrent read and write requirements ;4、 Efficient reading and writing of massive data ;
Non relational database MongoDb、redis、HBase	1、 Using key value pairs to store data ;2、 Distributed ;3、 In general, it does not support ACID characteristic ;4、 A non relational database is not strictly a database , It should be a collection of data structured storage methods .	1、 No need to go through sql Layer resolution , High read and write performance ;2、 Based on key value pair , The data is not coupled , Easy to expand ;3、 The format of data storage ：nosql The storage format is key,value form 、 Document form 、 Picture form and so on , Document form 、 Picture form and so on , Relational databases only support basic types .	1、 Does not provide sql Support , The cost of learning and using is high ;2、 No transactions , Additional features bi And reports and other support is not good ;

notes 1： Database transactions must have ACID characteristic ,ACID yes Atomic Atomicity ,Consistency Uniformity ,Isolation Isolation, ,Durability persistence .

notes 2： Persistent storage of data , Especially the persistent storage of massive data , Still need a relational database .

What is database management system (DataBase Management System abbreviation DBMS)：

 The so-called database management system is the computer software for managing data 

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Mainstream database management system ：

MySQL、Oracle、SQLite、Access、MS SQL Server etc.

　 All the above database management systems are a software , Both have two main functions ：

　　1. Save data to a file or memory

　　2. Receive specific commands , The file is then manipulated accordingly

Specific application scenarios and application fields of database management system

　mysql It is mainly used for large portals , For example, Sogou 、 Sina, etc , Its main advantage is open source , Because the open source database is free , He is now a product of Oracle .
　oracle Mainly used in banks 、 The railway 、 Airport, etc . The database is powerful , High software cost . It's also Oracle's product .
　sql server It's a Microsoft product , It is mainly used in large and medium-sized enterprises , Like Lenovo 、 Founder et al .

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　 Tables and records

What is a watch

　　　　　　 The so-called table has actually been mentioned above Is a specific file in the folder

　　　　 What is a record

　　　　　　 The so-called record refers to... In the file Information from multiple fields makes up a record , A line in a file

database server Database management system database The relationship between tables and records ( a key )

　 database server --- function ---> Database management software 

   Database management software ---> management ---> database 

   database --- organization ---> surface , It's a folder --- organization ---> file 

   surface --- Deposit ---> Multiple records , I.e. documents --- Deposit ---> Multi line content 　

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mysql Related introduction

What is? mysql

MySQL Is a relational database management system , The Swedish MySQL AB  Companies to develop , At present belongs to the  Oracle  A subsidiary company .MySQL  The most popular relational database management system , stay  WEB  Application aspect MySQL It's the best  RDBMS 
(Relational Database Management System, Relational database management system )  One of the application software .

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mysql It's just one. socekt Server side Client software 　　mysql Bring their own 　　python modular

Download and install

windows Version download

1 download

MySQL Community Server 5.7.16
  
http://dev.mysql.com/downloads/mysql/

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2、 decompression

If you want to MySQL Install in the specified directory , Then move the unzipped folder to the specified directory , Such as ：C:\mysql-5.7.16-winx64

3、 initialization

MySQL After decompression bin There are a lot of executable files in the directory , stay CMD Execute the following command to initialize the data ：

 Server side ：d:\mysql\mysql-5.7.16-winx64\bin(MySQL The installation path )\mysqld --initialize-insecure
    #  user name  root  password ： empty 

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4、 start-up MySQL service

stay CMD Execute commands in to start MySQL service

d:\mysql\mysql-5.7.16-winx64\bin\mysqld

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5、 start-up MySQL Client and connect MySQL service

Due to the 【mysqld –initialize-insecure】 command , It is not given by default root Account setting password

 Client connection ：
d:\mysql\mysql-5.7.16-winx64\bin\mysql -u root -p
#  Prompt for a password , Directly enter 

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Enter enter enter , The figure below shows that the installation is successful ：

Only this and nothing more ,MySQL The server has been installed successfully and the client can connect , Operate later MySQL when , Just repeat the above 4、5 Step by step . however , stay 4、5 It is cumbersome to repeatedly enter the executable file directory in step , If you want to be easy to operate in the future , You can do the following .

a. Add environment variables

take MySQL Executable files are added to environment variables , Thus, the execution command can be executed

【 Right click the computer 】--》【 attribute 】--》【 Advanced system setup 】--》【 senior 】--》【 environment variable 】--》【 Find... In the second content box   A variable called Path  A line , double-click 】<br> --> 【 take MySQL Of bin The directory path is appended to the variable value , use  ;  Division 】
  
 Such as ：
D:\mysql\mysql-5.7.16-winx64\bin

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In this way , When you start the service and connect later , Only ：

#  start-up MySQL service , Input... At the terminal 
mysqld
  
#  Connect MySQL service , Input... At the terminal ：
mysql -u root -p

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b. take MySQL Service production into windows service

The last step solved some problems , But not completely , Because it's executing 【mysqd】 start-up MySQL Server time , The current terminal will be hang live , Then make a setting to solve this problem ：

#  Make MySQL Of Windows service , Execute this command at the terminal ：
"d:\mysql\mysql-5.7.16-winx64\bin\mysqld" --install
  
#  remove MySQL Of Windows service , Execute this command at the terminal ：
"d:\mysql\mysql-5.7.16-winx64\bin\mysqld" --remove

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After registering as a service , Turn it on and off later MySQL The service , Simply execute the following command ：

#  start-up MySQL service 
net start mysql
  
#  close MySQL service 
net stop mysql

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Linux Version download

1. install ：

yum install mysql-server　

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2. Server startup

mysql.server start

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3. Client connection

 Connect ：
    mysql -h host -u user -p
  
     Common mistakes ：
        ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2), it means that the MySQL server daemon (Unix) or service (Windows) is not running.
 sign out ：
    QUIT  perhaps  Control+D

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