MySQL Express - day 1 - basic introduction

MySQL Fast track

( One )、MySQL First time to know

1.1、 Database introduction

Database introduction ：

 Database is organized according to data structure , Warehouse for storing and managing data . It is a collection of large amounts of organized, sharable and uniformly managed data stored in computers for a long time 

1.2、 Classification of database ：

1. Relational database （SQL）    The relationship between tables 
    Oracle、MySQL、SQLSever
2. Non relational database （NoSQL：NOt Snly SQL）    Data is stored in the database in the form of objects , Usually, the  key value There is a form of 
    MongoDB、Redis

1.3、MySQL

1.3.1、MySQL brief introduction ( Fast operation )

. . MySQL Is a relational database management system , The Swedish MySQL AB Companies to develop , At present belongs to the Oracle company .MySQL It's an associated database management system , The associated database keeps the data in different tables , Instead of putting all the data in one big warehouse , This increases speed and flexibility .

1.3.2、MySQL Characteristics

1. MySQL It's open source. , So you don't have to pay extra ;
2. MySQL Support large databases . Can handle large databases with tens of millions of records ;
3. MySQL standards-of-use SQL Data language form ;
4. MySQL It can be installed on different operating systems , And provide the operation interface of multiple programming languages ;
5. stay WEB Application aspect ,MySQL Have a good performance .

1.3.3、MySQL Interactive mode ( Server side ： service + Storage engine )

    MySQL Database is a kind of c/s( client / Server side ) Structured software , If you want to access the server, you must use the client ( The server has been running , The client runs when it needs to be used )
    1、 Client connection authentication ： Link server , Authentication 
    2、 The client sends SQL command 
    3、 Server receive SQL Instructions , Handle SQL Instructions 、 Return operation result 
    4、 The client receives the result , Show results .

1.3.4、 Database objects

     From a macro point of view MySQL The internal objects of the server are divided into four layers ： System (DBMS)-> database (DB)—> Data sheet (Tables)-> Field (fieid)

1.3.4.1、SQL Introduce

SQL（Structured Query Language） Structured query language , It is mainly divided into three parts ：

1、DDL（Data Definition Language）： Data definition language , Used to maintain the structure of stored data （ database 、 surface ）. For instructions ：
    create、drop、alter etc. .
2、DML（Data Manipulation Language）： Data operation language , It is mainly used to operate data （ What's in the data table ）. For instructions ：
    insert、delete、update etc. .
3、 among  DML  There is a separate classification inside  - DQL（Data Query Language） Data query language , Such as  select. because 99% It's a query operation .

1.3.4.2、 Database basic command

     Show the current mysql edition 
        SELECT VERSION();
     Display the current system time 
        SELECT NOW();
     Show current user 
        SELECT USER();
     view the database 
        SHOW databases;  --show( Show ) databases( database ) 

1.3.4.3、MySQL Grammatical norms

1、 Keywords and function names are all capitalized （ Lowercase can also be recognized , But lowercase is not good for distinguishing keywords from functions , So it is recommended to use upper case ）
2、 Database name 、 Table name 、 Field names are all lowercase
3、SQL The statement must end with a semicolon

1.3.4.4、 Database operation command

    1、 Create database （ No addition s）
        CREATE DATABASE  Database name ;
    2、 view the database ( Add s)
        SHOW DATABASES;
    3、 Select the specified database 
        USE  Database name ;
    4、 Delete database 
        DROP DATAVABASE  Database name ;

1.3.4.5、 Data table operation command （ library ：database surface ：table Field ：column）

 
    1、 Create table 
        CRETAE TABLE  Table name ( Field ,  Field properties ,...);
		#  demonstration 
        create table User_Stu(ID int(10), name varchar(10), age int, sex varchar(10));
        #  perhaps 
        CRETAE TABLE USER(
            ID INT(10),
            NAME VARCHAR(10),
            age INT,
            sex VARCHAR(10)  -- There is no comma 
            );
        
    2、 View all tables 
        SHOW TABLES;
        
    3、 View a single table 
        DESCRIPTION  Table name ;   It can be abbreviated desc +  Table name 
        
    4、 Delete table 
        DROP TABLE  Table name ;
        drop table user1;  -- Delete table user1
        
    5、 Modify the name of the table 
        RENAME TABLE  The old name of the table  TO  The new name of the table ;
        ALTER TABLE RENAME  The old name of the table  TO  The new name of the table ;
        
    6、 Modify table type 
        ALTER TABLE  The name of the table  MODIFY  Field   Field definition ;
        alter table user_stu modify name_ID varchar(10);  -- user_stu Tabular name_ID The type changes to varchar(10);
        
    7、 Modify fields 
        a、 newly added 
            ALTER TABLE  The name of the table  ADD COLUMN  Field   Field definition ;
            alter table user_stu add modify name_ID int(10);  --user_stu A new field is added to the table , Field called name_ID  The type is int
            
        b、 modify 
            ALTER TABLE  The name of the table  CHANGE  Old fields   The new fields   Field definition ;
            # change  And  MODIFY  The difference between :change You can change the name , But it needs to be written twice 
            
        c、 Delete 
            ALTER TABLES  The name of the table  DROP COLUMN  Field name ;
            alter table user1 orop ID;  -- Delete user1 Tabular id Column