[MySQL basics]

Database Overview

Common database concepts

One 、 Memory uses low voltage and high voltage to distinguish 0 and 1 Data storage , So it can't be stored when the power is off , What should we do if we want to store data persistently ？ With the help of relevant media

1. Stored in related files ： Pictures are stored in jpg In file , The text is stored in .doc In file ,Java The source code exists .java In file
2. Complex data is stored in a database
3. Other media

Persistence (persistence)： Save data to a power down storage device for later use . Most of the time , Especially for enterprise applications , Data persistence means saving the data in memory to the hard disk ” curing ”, The implementation process of persistence is mostly accomplished through various relational databases .
The main function of persistence is to store the data in memory in the relational database , Of course, it can also be stored in disk files 、XML In the data file .

Two 、 Why use a database ： Database can realize data persistence
3、 ... and 、 The characteristics of database ：

1. The amount of data stored is huge
2. There are many types of data that can be stored

Four 、 Relevant concepts ：

1. DB： Full name database （Database）, It's about storing data “ Warehouse ”, Its essence is a file system . It holds a series of organized data . It is essentially a file that holds data
2. DBMS： Full name: database management system （Database Management System）, It is a kind of large-scale software for manipulating and managing database , For building 、 Use and maintain database , Manage and control the database in a unified way . The user accesses the data in the table in the database through the database management system . Such as MySQL

Scenes in life ： You wrote a .doc file , Do you use word To open it ,.doc The document is equivalent to the database here DB,word It is equivalent to the database management system here DBMS

3. SQL： The full name is structured query language （Structured Query Language）, It's a language for communicating with databases .

We use SQL Language coding makes DBMS Help us go to the database DB Do some operations in

5、 ... and 、 Database management system DBMS You can manage multiple databases , Generally, developers will create a database for each application . To save the data of the entity in the application , In general, multiple tables will be created in the database , To save the data of entity users in the program .

MySQL Introduce

One 、MySQL It's an associated database management system , Save the data in different tables , Instead of putting all the data in one big warehouse , This increases speed and flexibility .
Two 、MySQL It can be customized , Adopted GPL（GNU General Public License） agreement , You can modify the source code to develop your own MySQL System .
3、 ... and 、MySQL Support large databases . Can handle large databases with tens of millions of records .32 Bit system table files can support 4GB ,64 The largest table file supported by bit system is 8TB .
Four 、MySQL Use The standard SQL Data language form .
5、 ... and 、 Why choose MySQL：

1. Open source , Low use cost .
2. Performance is remarkable , Stable service .
3. The software is small , Easy to use , And easy to maintain .
4. Has a long history , Community users are very active , Ask for help when you have problems .
5. Many Internet companies are using , After the verification of time .

6、 ... and 、Oracle And MySQL Compare

1. Oracle It is more suitable for large multinational enterprises , Because they are not cost sensitive , But there are higher requirements for performance and safety .
2. MySQL Because of its small size 、 Fast 、 Low total cost of ownership , A large database that can handle tens of millions of records , Especially open source , Makes many Internet companies 、 Small and medium-sized websites choose MySQL As website database （Facebook,Twitter,YouTube, Alibaba / The ant gold dress , Where are you going? , Meituan takeout , tencent ）.

RDBMS And non RDBMS Compare

Relational database RDBMS

One 、 This type of database is the oldest database type , Relational database model is to reduce the complex data structure to simple Binary relationship （ namely Two dimensional tabular form ）.
Two 、 Relational database to line （row） And column （column） In the form of data storage . This series of rows and columns is called a table （table）, A set of tables form a library （database）
3、 ... and 、 The data records between tables are related （relationship）. All kinds of entities in the real world and the relationships between them are represented by relational models . Relational database is a database based on relational model .
Four 、SQL It is the query language of relational database
5、 ... and 、 advantage ：

1. Complex queries ： It can be used SQL Statement is convenient to do very complex data query between one table and multiple tables .
2. Transaction support ： So that the data access requirements with high security performance can be realized .

Non relational database RDBMS

One 、 Relational databases have been able to solve most of the problems , In some cases, we need to discard some functions to meet higher requirements . Non relational databases discard the feature of storing rich data , Higher performance has been achieved
Two 、MySQL Operating relational databases ,NoSQL Operate on non relational databases

Key database

Key value database through Key-Value Key value to store data , among Key and Value It can be a simple object , It can also be a complex object .Key As a unique identifier , The advantage is that the search speed is fast , In this respect, it is obviously better than relational database , The disadvantage is that you can't use conditional filtering like a relational database （ such as WHERE）, If you don't know where to find the data , You have to traverse all the keys , This will consume a lot of computation . The typical usage scenario of key value database is as memory cache . Redis Is the most popular key value database .

Document database

This kind of database can store and obtain documents , It can be XML、JSON Equiform . In a database, a document is the basic unit for processing information , A document is a record . Documents stored in the document database , It is equivalent to that stored in the key value database “ value ”.MongoDB Is the most popular document database . Besides , also CouchDB etc. .

Search engine database

Although relational database adopts index to improve retrieval efficiency , However, the efficiency of full-text indexing is low . Search engine database is a data storage form applied in the field of search engine , Because search engines crawl a lot of data , And stored in a specific format , In this way, the best performance can be guaranteed when searching . The core principle is “ Inverted index ”.
Typical products ：Solr、Elasticsearch、Splunk etc. .

Columnar database

A column database is a database relative to a row store ,Oracle、MySQL、SQL Server And so on the database all uses the line type storage （Row-based）, The columnar database is to store data into the database according to columns , The advantage of this is that it can reduce the system greatly I/O, Suitable for distributed file systems , The disadvantage is that the function is relatively limited . Typical products ：HBase etc. .
Suppose we want to query the information of some fields of a record in the database , For example, I just want to check the age of Zhang San , I don't need to know his gender 、 Professional and so on , If you use a database based on row storage , All the data of Zhang San will be loaded into memory during query , Will load useless information , So that means we have done a lot of redundant IO, Low performance . But if the columnar database is used to store data , Then I only need to query the column of the field you want .

If there is 100 personal , There is only one person 20 A field , Is it more efficient to use row storage ？

Graphic database

The data structure of graph is used to store entities （ object ） The relationship between , The most typical example of graphical database is the relationship between people in social networks , The data model is mainly based on nodes and edges （ Relationship ） To achieve , The feature is that it can efficiently solve complex relationship problems
Graphic database as the name suggests , It is a database that stores graphical relationships . It uses the data structure of graph to store entities （ object ） The relationship between . Relational data is used to store data with explicit relationships , But for the data storage of complex relationships, it is not enough . Such as the relationship between characters in social networks , If you use a relational database, it is very complex , Using a graphics database will be very simple . Typical products ：Neo4J、InfoGrid etc. .

Relational database design rules

One 、 The typical data structure of relational database is data table , The composition of these data tables is structured
Two 、 Put the data in the table , Put the watch in the library
3、 ... and 、 There can be multiple tables in a database , Every watch has a name , To identify yourself . Table names are unique .
Four 、 Table has some characteristics , These properties define how data is stored in tables , similar Java and Python in “ class ” The design of the .

surface 、 Record 、 Field

One 、 The relationship between tables is expressed in E-R Model to describe .E-R（entity-relationship, Entity - contact ） There are three main concepts in the model ： Entity set 、 attribute 、 Contact set .

Entity set ： surface
attribute ： Fields in the table
Contact set ： The relationship between records in a table and records in another table

Two 、 A set of entities （class） Corresponding to a table in the database （table）, An entity （instance） It corresponds to a row in the database table （row）, Also known as a record （record）. An attribute （attribute） Corresponds to a column in the database table （column）, Also known as a field （field）.

A relation corresponding to the operation of a database in a programming language , This relationship we call ORM mapping
ORM thought (Object Relational Mapping) reflect ：
A table in the database <——> Java or Python A class in
A piece of data in the table <——> An object in a class （ Or entity ）
A column in the table <——> A field in a class 、 attribute (field)

The relationship between tables

One 、 The data records between tables are related （relationship）. All kinds of entities in the real world and the relationships between them are represented by relational models .
Two 、 Four kinds of ： One to one connection 、 One to many connection 、 Many to many connection 、 Self quoting

One to one connection （one-to-one）

One 、 One to one connection ： surface A A record in the corresponding table B One of the records
Two 、 There are not many applications in the actual development , Because one-to-one can be created as a table .

give an example ： Design a student list ： Student number 、 full name 、 Phone number 、 class 、 Is don't 、 Id card number 、 Home address 、 Native place 、 Emergency contact 、… There are so many fields , We can split it into two tables , The records of the two tables are one-to-one correspondence .
Basic information table （ Frequently used information ）： Student number 、 full name 、 Phone number 、 class 、 Is don't
File information table （ Infrequent information ）： Student number 、 Id card number 、 Home address 、 Native place 、 Emergency contact 、…
If you don't dismantle it , Every time we query, we will load many unnecessary fields , For example, infrequently used information is often loaded in , After the disassembly, I will query every time （ No ） Frequently used information , Reduce the loading of redundant information , Reduce IO, Improve performance

3、 ... and 、 Two principles of table building ：
The foreign key is unique ： Primary key of master table and foreign key of slave table （ only ）, Form the main foreign bond relationship , The foreign key is unique .
The foreign key is the primary key ： Primary key of master table and primary key of slave table , Form the main foreign bond relationship .

One-to-many relation （one-to-many）

One 、 surface A A record in the corresponding table B Multiple records in
Two 、 Common instance scenarios ： Customer and order forms , Classification table and commodity table , Department tables and staff tables .

give an example ：
The employee table ： Number 、 full name 、…、 Department
Departmental table ： Number 、 name 、 brief introduction
The Department table stores the records of each department , There can be more than one employee in a department , That is, one record corresponds to multiple employees

3、 ... and 、 One to many tabulation principle ： From table ( In many ways ) Create a field , The field points to the main table as a foreign key ( a party ) Primary key of

Many to many （many-to-many）

One 、 To represent a many to many relationship , You must create a third table , This table is often called a join table , It divides many to many relationships into two one to many relationships . Insert the primary keys of both tables into the third table .
Two 、 give an example

1. Student - Course
   Student information sheet ： One line represents a student's information （ Student number 、 full name 、 Phone number 、 class 、 Is don't …）
   Course information sheet ： One line represents the information of a course （ Course number 、 Teaching teacher 、 brief introduction ……）
   Course selection information table ： A student can take multiple courses , A course can be chosen by more than one student
2. product - Order ：“ Order ” Table and “ product ” Tables have a many to many relationship , This relationship is achieved through a relationship with “ The order details ” A table is defined by establishing two one to many relationships . One order can have multiple products , Each product can appear in multiple orders .
   Product list ：“ product ” Each record in the table represents a product .
   The order sheet ：“ Order ” Each record in the table represents an order .
   Order details ： Each product can be combined with “ Order ” Multiple records in the table correspond to , That is, it appears in multiple orders . An order can be made with “ product ” Multiple records in the table correspond to , That is, it contains multiple products .
3. user - role
   Many to many relationship table building principle ： You need to create a third table , At least two fields in the middle table , These two fields are used as foreign keys to each other's primary keys .

Self quoting

Quote yourself , The following table ：

MySQL Environment building

MySQL The uninstall

Step one ： stop it MySQL service

Before uninstalling , First stop MySQL8.0 Service for . Press on the keyboard “Ctrl + Alt + Delete” Composite key , open “ Task manager ” Dialog box , Can be in “ service ” List found “MySQL8.0” Service for , If now “ Running ” state , You can right-click Services , choice “ stop it ” Option stop MySQL8.0 Service for , As shown in the figure .

Step two ： Software uninstall

The way 1： Via control panel

uninstall MySQL8.0 Your application can be directly in the same way as other desktop applications “ Control panel ” choice “ Uninstall program ”, And find... In the program list MySQL8.0 Server program , Double click uninstall directly , As shown in the figure .

Delete in this way , The data in the data directory will not be deleted .

The way 2： adopt 360 Or software such as computer manager

A little

The way 3： Uninstall through the uninstall function provided by the installation package

You can also use the installation wizard to MySQL8.0 Uninstall the server program .

1. Double click the downloaded... Again mysql-installer-community-8.0.26.0.msi file （ That is, the software installation package ）, Open the setup wizard . The setup wizard will automatically detect installed MySQL Server program .
   
   And then execute ：
   
2. Select the to uninstall MySQL Server program , single click “Remove”（ remove ）, You can uninstall .
   
3. single click “Next”（ next step ） Button , Confirm uninstall .
   
4. A window will pop up to select whether to remove the data directory at the same time . If you want to delete MySQL Data in the server , Then check “Remove the data directory”, As shown in the figure .
   
5. Perform the uninstall . single click “Execute”（ perform ） Button to unload .
   
6. Uninstall complete . single click “Finish”（ complete ） button . If you want to uninstall at the same time MySQL8.0 Installation wizard for , Check “Yes,Uninstall MySQL Installer” that will do , As shown in the figure .
   

Step three ： Cleaning of residual files

One 、 If the installation is not successful again , You can uninstall and clean up the residual files before installing .

1. Service catalog ：mysql The installation directory of the service
2. Data directory ： Default in C:\ProgramData\MySQL
   If you have specified the data directory separately , Just find your own data directory and delete it .

Be careful ： Please make data backup before unloading

Two 、 After the operation , Need to restart the computer , Then install it . If the installation still fails , You need to continue with the following steps 4.

Step four ： Clean up the registry （ Choose to do ）

One 、 If you did the previous steps , The installation failed again , Then you can clean the registry .
Two 、 How to open the registry editor ： In the system's search box （win+r） Input in regedit

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\Eventlog\Application\MySQL service   Directory delete 
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\MySQL service   Directory delete 
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\Eventlog\Application\MySQL service   Directory delete 
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Services\MySQL service   Directory delete 
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Eventlog\Application\MySQL Service directory delete 
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MySQL Service deletion 

Be careful ： In the registry ControlSet001,ControlSet002, Is not necessarily 001 and 002, May be ControlSet005、006 And so on

Step five ： Delete the environment variable configuration

One 、 find path environment variable , Put it all about mysql Delete the environment variable of , Remember not to delete all . for example ： Delete D:\develop_tools\mysql\MySQLServer8.0.26\bin; This part

MySQL The download 、 install 、 To configure

One 、MySQL Of 4 The big version

1. MySQL Community Server Community version , Free open source , Free download , But no official technical support , Suitable for most ordinary users .
2. MySQL Enterprise Edition Enterprise version , Pay for , Can't download online , You can try 30 God . It provides more functions and more complete technical support , It is more suitable for enterprise customers with high requirements for database function and reliability .
3. MySQL Cluster Cluster version , Free open source . It is used to set up cluster servers , You can put a few MySQL Server Encapsulate into a Server. It needs to be used on the basis of community version or enterprise version .
4. MySQL Cluster CGE Advanced clustering , Pay for .

Two 、 Used in this course 8.0.26 edition .
3、 ... and 、 Officials also provide MySQL Workbench（GUITOOL） One for MySQL Designed graphical interface management tool .MySQLWorkbench It's divided into two versions , Namely Community Edition （MySQL Workbench OSS）、 Commercial version （MySQL WorkbenchSE）.

download

One 、 Download address ： Official website
Two 、 Open the website , Click on DOWNLOADS, then , Click on MySQL Community(GPL) Downloads

3、 ... and 、 Click on MySQL Community Server

Four 、 stay General Availability(GA) Releases Select the appropriate version

Windows Two installation files are provided under the platform ：MySQL Binary distribution （.msi The installation files ） And installation free version （.zip Compressed files ）. In general , Binary distributions should be used , Because this version provides a graphical installation wizard process , Easier to use than other distributions , You don't need other tools to start to run MySQL.
Here it is Windows It is recommended to download MSI Erection sequence ; Click on Go to Download Page Download it
5、 ... and 、Windows Under the MySQL8.0 There are two installers installed

1. mysql-installer-web-community-8.0.26.0.msi Download program size ：2.4M; Networking installation components are required during installation .
2. mysql-installer-community-8.0.26.0.msi Download program size ：450.7M; Offline installation during installation, i.e
   can . recommend .
   
   If installed MySQL5.7 Version! , choice Archives You can select the historical version in it , Then choose MySQL5.7 The corresponding version of . Download the latest MySQL5.7.34 edition .

install

MySQL When the download is complete , Find the download file , Double click to install , The specific operation steps are as follows .

1. Double-click the downloaded mysql-installer-community-8.0.26.0.msi file , Open the setup wizard .
2. open “Choosing a Setup Type”（ Choose the installation type ） window , It lists 5 Installation types , Namely Developer Default（ Default installation type ）、Server only（ Just as a server ）、Client only（ Just as a client ）、Full（ Completely installed ）、Custom（ Custom installation ）. Choose here “Custom（ Custom installation ）” Type button , single click “Next( next step )” Button .
   
3. open “Select Products” （ Choose products ） window , You can customize the list of products to be installed . for example , choice “MySQL Server 8.0.26-X64” after , single click “→” Add a button , You can choose to install MySQL The server , As shown in the figure . Adopt a general method , You can add other products you need to install .
   
   At this point, if you directly “Next”（ next step ）, The installation path of the product is the default . If you want to customize the installation directory , You can select the corresponding product , Then it will appear below “Advanced Options”（ Advanced options ） Hyperlinks for .
   
   single click “Advanced Options”（ Advanced options ） The installation directory selection window will pop up , As shown in the figure , At this point, you can set it separately MySQL Server program installation directory and data storage directory . If not set , By default, they are in C Discoid Program Files Contents and ProgramData Catalog （ This is a hidden Directory ）. If you customize the installation directory , Please avoid “ chinese ” Catalog . in addition , It is recommended that the service directory and data directory be stored separately .
   
4. After selecting the product to install in the previous step , single click “Next”（ next step ） Enter the confirmation window , As shown in the figure . single click “Execute”（ perform ） Button to start installation .
   
5. After the installation is completed, please wait “Status”（ state ） Below the list will be displayed “Complete”（ installation is complete ）, As shown in the figure .
   

MySQL8.0 To configure

MySQL After installation , You need to configure the server . The specific configuration steps are as follows .

1. In the last step of the previous section , single click “Next”（ next step ） Button , You can enter the product configuration window .
   
2. single click “Next”（ next step ） Button , Get into MySQL Server type configuration window , As shown in the figure . Generally, the default port number is selected 3306
   
   among ,“Config Type” Option is used to set the type of server . Click the bottom triangle button to the right of the option , You can view it 3 An option , As shown in the figure .
   
   Development Machine（ Developing machines ）： This option represents a typical personal desktop workstation . At this point, multiple applications need to run on the machine , that MySQL The server will use the least system resources
   Server Machine（ The server ） ： This option represents the server ,MySQL The server can run with other server applications , for example Web The server etc. .MySQL The server is configured with an appropriate proportion of system resources .
   Dedicated Machine（ Dedicated server ） ： This option represents run only MySQL Servers served .MySQL The server is configured to use all available system resources .
3. single click “Next”（ next step ） Button , Open the set authorization mode window . among , The options above are MySQL8.0 New ways of Authorization , use SHA256 Basic cryptographic methods ; The following options are traditional authorization methods （ Retain 5.x Version compatibility ）.
   
4. single click “Next”（ next step ） Button , Open setup server root Super administrator password window , As shown in the figure , You need to enter the same login password twice . It can also be done through “Add User” Add other users , When adding other users , You need to specify a user name 、 The user name is allowed on which computer / Which hosts log in , You can also specify user roles, etc . Users will not be added here , User management in MySQL Advanced features .
   
5. single click “Next”（ next step ） Button , Open the set server name window , As shown in the figure . The service name will appear in Windows In the list of services , You can also use the service name in the command line window to start and stop the service . This article sets the service name to “MySQL80”. If you want to start the self starting service , You can also check “Start the MySQL Server at System Startup” Options （ recommend ）.
   Here is how to run the service ？ You can choose “Standard System Account”（ Standard system users ） perhaps “Custom User”（ Custom user ） One of them . The former is recommended here .
   
6. Click click “Next”（ next step ） Button , Open the confirm settings server window , single click “Execute”（ perform ） Button
   
7. Complete the configuration , As shown in the figure . single click “Finish”（ complete ） Button , The configuration of the server can be completed .
   
8. If there are other products that need to be configured , You can choose other products , Then continue to configure . without , Direct selection “Next”（ next step ）, Directly complete the whole installation and configuration process .
   
9. End installation and configuration .
   

MySQL5.7 install 、 To configure

One 、 install ： The installation process of this version is the same as the above process, except that the version number is different , Other links are the same . So we omit MySQL5.7.34 Screenshot of version installation .
Two 、 To configure ： Configuration phase and MySQL8.0 The version is slightly different . In most cases, choose directly “Next” that will do , It does not affect the finishing and use . Configuration here MySQL5.7 when , Focus on ： With the previously installed MySQL8.0 You cannot use the same port number .

Installation failure problem

One 、 problem 1： Unable to open MySQL8.0 Software installation package or failure during installation , How to solve ？
Running MySQL8.0 Before installing the package , Users need to ensure that... Is installed in the system .Net Framework Related software , If this software is missing , Will not install properly MySQL8.0 Software .

Solution ： To here download Microsoft .Net Framework 4.5 And after installation , Then go install MySQL. in addition , Also make sure Windows Installer normal setup .windows Installation on mysql8.0 The operating system needs to be installed in advance Microsoft Visual C++ 2015-2019.


The solution is still to Microsoft official website Download the corresponding environment
Two 、 Unload and reload MySQL Failure ？
The problem is usually due to MySQL When uninstalling , Not completely clear the relevant information .
Solution ： Delete the previous installation directory . If the service installation directory has not been specified separately in the previous installation , The default installation directory is C:\Program Files\MySQL, Completely delete the directory . At the same time to delete MySQL Of Data Catalog , If the data directory has not been specified separately in the previous installation , The default installation directory is C:\ProgramData\MySQL, This directory is generally hidden . After deleting , Just reinstall .
3、 ... and 、 How to be in Windows The system deletes the previously uninstalled clean MySQL List of services ？
In system “ Search box ” Input in “cmd”, Press “Enter”（ enter ） Key confirmation , The command prompt interface pops up . Then input “sc delete MySQL service name ”, Press “Enter”（ enter ） key , You can completely delete the remaining MySQL Yes .

Configure environment variables

If you don't configure MySQL environment variable , You can't type... Directly on the command line MySQL Login command . Here's how to configure MySQL Environment variables of ：

1. Right click on the desktop 【 This computer 】 Icon , Choose... From the shortcut menu that pops up 【 attribute 】 The menu command .
2. open 【 System 】 window , single click 【 Advanced system setup 】 link .
3. open 【 System attribute 】 Dialog box , choice 【 senior 】 tab , And then click 【 environment variable 】 Button .
4. open 【 environment variable 】 Dialog box , Select... In the system variable list path Variable .
5. single click 【 edit 】 Button , stay 【 Edit environment variables 】 In the dialog box , take MySQL Application's bin Catalog （C:\ProgramFiles\MySQL\MySQL Server 8.0\bin） Add to variable value , Separate it from other paths with semicolons .
6. Add after completion , single click 【 determine 】 Button , This completes the configuration path Variable operation , Then you can directly enter MySQL Command to log in to the database .

Service startup 、 Sign in

Start and stop of service

One 、MySQL After installation , The server process needs to be started , Otherwise, the client cannot connect to the database .
Two 、 In the previous configuration process , Have already put MySQL Installed as Windows service , And check when Windows start-up 、 When it stops ,MySQL It also starts automatically 、 stop it .

Use GUI tools

1. open windows service
   The way 1： Computer （ Right click ）→ management （ Click on ）→ Services and Applications （ Click on ）→ service （ Click on ）
   The way 2： Control panel （ Click on ）→ Systems and security （ Click on ）→ Management tools （ Click on ）→ service （ Click on ）
   The way 3： The task bar （ Right click ）→ Start task manager （ Click on ）→ service （ Click on ）
   The way 4： single click 【 Start 】 menu , Type in the search box “services.msc”, Press Enter Key confirmation
2. find MySQL80（ Right click ）→ To start or stop （ Click on ）
   

Use command line tools

#  start-up  MySQL  The service command ：
net start MySQL service name 
#  stop it  MySQL  The service command ：
net stop MySQL service name 

explain ：

1. start and stop The following service name should be consistent with the service name specified during previous configuration .
2. If when you enter a command , Tips “ Denial of service ”, Please open the command prompt interface as the system administrator and try again .

Login and exit of the built-in client

When MySQL After service startup , You can log in through the client MySQL database . Be careful ： Confirm that the service is on .

MySQL It comes with its own client

The start menu → All the procedures → MySQL → MySQL 8.0 Command Line Client

explain ： Is limited to root user

Windows Command line

Format ：mysql -h Host name -P Port number -u user name -p password
give an example ：mysql -h localhost -P 3306 -u root -pabc123 # Here I set root The user's password is abc123
explain ：

1. -p There must be no space between and password , There may or may not be spaces between other parameter names and parameter values . Such as ：mysql -hlocalhost -P3306 -uroot -pabc123
2. The writing order is not required
3. It is recommended to enter the password on the next line , Keep it safe

mysql -h localhost -P 3306 -u root -p
Enter password:****

4. The client and server are on the same machine , So the input localhost perhaps IP Address 127.0.0.1. meanwhile , Because it is connected to this machine ： -hlocalhost You can omit , If the port number has not been modified ：-P3306 You can omit it , Abbreviation ：

mysql -u root -p
Enter password:****

After successful connection , About MySQL Server Service version information , And the number of connections id identification . It can also be done on the command line through c:\> mysql -V or c:\> mysql --version obtain MySQL Server Service version information . Or after login , adopt mysql> select version(); View current version information .

Log out

exit or quit

MySQL Demonstrate the use of

Launch and log in mysql After use

View all databases

Format ：show databases;

explain ：

1. information_schema yes MySQL The database of the system , The main preservation is MySQL System information of database server , For example, the name of the database 、 The name of the data table 、 Field name 、 Access rights 、 Data files The folder and the folder used by the system , wait
2. performance_schema yes MySQL The database of the system , Can be used to monitor MySQL Various performance indexes .
3. sys database yes MySQL The database of the system , The main function is to show... In a more understandable way MySQL Various performance indexes of database server , Help system administrators and developers monitor MySQL Technical performance .
4. mysql The database holds MySQL System information required by the database server to run , Such as data folders 、 Currently in use Character set 、 Constraint check information , wait

Create your own database

Format ：create database Database name ;. for example , establish dbtest1 database ：create database dbtest1;, The name cannot be the same as an existing database .

Using a database

Format ：use Database name ;. for example , Use dbtest1 database ：use dbtest1;

explain ： If not used use sentence , The following operations on the database do not add “ Data name ” The limit of , Then it will be reported. “ERROR 1046 (3D000): No database selected”( No database selected ), Use up use After statement , If the next SQL They are all aimed at a database operation , Then don't repeat use 了 , If you want to operate on another database , Then we have to re use. As shown in the following figure, create a table directly after creating a database , Not used use Using a database

View all tables in a library

Format ：show tables from Database name ;

Create a new table

create table  The name of the table ( 
	 Field name   data type ,
	 Field name   data type 
);

For example, create an employee table ：

create table employees(
	id int,
	name varchar(20) # The longest name is no more than 20 Characters  
);

explain ： If it is the last field , You don't have to add a comma after it , Because the comma is used to separate each field .

View the data of a table

Format ：select * from Database table name ;. for example , View the data of the employee table ：select * from employees;

Add a record to the table

One 、 Format ：insert into The name of the table values( List of values );. for example , Add two records to employees In the table ：insert into employees values(1,'cara');.
Two 、 But if 5.7 The version is written in Chinese ：insert into employees values(1,' Zhang San '); insert into employees values(2,' Li Si '); Will report a mistake ：

mysql> insert into employees values(1,' Zhang San ');
ERROR 1366 (HY000): Incorrect string value: '\xD5\xC5\xC8\xFD' for column 'name' at row 1
mysql> insert into employees values(2,' Li Si ');
ERROR 1366 (HY000): Incorrect string value: '\xC0\xEE\xCB\xC4' for column 'name' at row 1

This is a character set problem , Because the character set you are using now is the default latin, No utf-8, Unable to recognize Chinese .
3、 ... and 、 The following code can view the database default character set ：

show variables like 'character_%';# View the default character set used by the database 
show variables like 'collation_%';# View character sorting comparison rules 

Four 、 Solution ： Change the default character set

1. modify MySQL Under the data directory of my.ini The configuration file ：

[mysql] # Around the 63 Row or so , Add under ：
...
default-character-set=utf8 # Default character set 
[mysqld] #  In about 76 Row or so , Add under 
...
character-set-server=utf8
collation-server=utf8_general_ci

Be careful ： It is recommended to modify the configuration file to use notepad++ And other advanced text editors , After opening and modifying with software such as Notepad, the file code may be changed to “ contain BOM head ” The coding , Thus, the service restart fails .

2. restart MySQL
3. Check if the setting is successful , The following configuration succeeded , Then we can create a new database 、 Create a new data table , Then add the data containing Chinese , If you have a previous database 、 The data table is still used latin, Cannot add Chinese data .
   

5、 ... and 、 stay MySQL 8.0 Before the release , The default character set is latin1,utf8 The character set points to utf8mb3. Website developers often change the code to utf8 Character set . If you forget to change the default code , There will be a problem of garbled code . from MySQL 8.0 Start , The default code of the database is changed to utf8mb4 , Thus, the above garbled code problem is avoided .

View the table creation information

Format ：show create table The name of the table \G. for example , see employees Table creation details ：show create table employees\G

View database creation information

Format ：show create database Database name \G. for example , see dbtest1 Database creation details ：show create database dbtest1\G

Delete table

Format ：drop table The name of the table ;. for example , Delete student table ：drop table student;

Delete database

Format ：drop database Database name ;. for example , Delete atguigudb database ：drop database atguigudb;

MySQL Directory structure and source code

Main directory structure

MySQL Directory structure of	explain
bin Catalog	all MySQL The executable of . Such as ：mysql.exe
MySQLInstanceConfig.exe	Database configuration wizard , What appears during installation
data Catalog	The directory where the system database is located
my.ini file	MySQL The main configuration file for
c:\ProgramData\MySQL\MySQL Server 8.0\data\	The directory of the database created by the user

MySQL Source code acquisition

First , You have to enter MySQL Download Interface . Here you don't choose to use the default “Microsoft Windows”, But through the drop-down bar , find “Source Code”, In the following operating system version , choice Windows（Architecture Independent）, Then click download . Next , Unzip the downloaded compressed file , We got it MySQL Source code . The source code can be opened and viewed with Notepad , If you have C++ Development environment of , You can also open and view... In the development environment .MySQL yes C++ Developed by , Let me briefly introduce the composition of the source code ：

1. sql The subdirectory is MySQL Core code ;
2. libmysql Subdirectories are client programs API;
3. mysql-test Subdirectories are test tools ;
4. mysys Subdirectories are operating system related functions and auxiliary functions ;

Common problems and solutions

root User password forgotten , Reset operation

Solution ：

1. Through task manager or service management , Turn off the mysqld（ Service process ）
2. From the command line + Special parameters on mysqld：mysqld -- defaults-file="D:\ProgramFiles\mysql\MySQLServer5.7Data\my.ini" --skip-grant-tables
3. here ,mysqld The service process has been opened . And no permission check is required
4. mysql -uroot No password login server . Start another client for
5. Modify the permission table ：

use mysql;
update user set authentication_string=password(' New password ') where user='root' and Host='localhost';
flush privileges;

6. Through task manager , Turn off the mysqld Service process .
7. Again through service management , open mysql service .
8. You can log in with the new password after modification .

mysql Order newspaper “ Not an internal or external command ”

hold mysql Installation directory bin Directory configuration to environment variables path in .

error error： Operate tables and data without selecting a database

Report errors ：ERROR 1046 (3D000): No database selected
Solution ：

1. Is the use of USE Database name ; sentence , In this way, the following statements will operate on the database by default
2. That is, all table objects are preceded by database .

The character set problem of the command-line client

mysql> INSERT INTO t_stu VALUES(1,' Zhang San ',' male ');
ERROR 1366 (HY000): Incorrect string value: '\xD5\xC5\xC8\xFD' for column 'sname' at
row 1

reason ： The server thinks your client's character set is utf-8, In fact, the character set of your client is GBK.

See all character sets ：SHOW VARIABLES LIKE 'character_set_%';

Solution ： Set the client character set of the current connection ：SET NAMES GBK;. If you're using cmd：

Modify the character encoding of databases and tables

See above