Today we begin to contact a new language Sql Language , stay 21 century , The most valuable thing is data , Should we take some of these data and store them ,Sql Language is such a container for storing data , Today, let's explore Sql The true face of Lushan ！！！

Database Overview

1. Why study databases ：

● Realize data persistence to local ;

● Use a complete management system for unified management , It can realize structured query , Easy to manage ;

2. Database related concepts ：

• DB： database （DataBase）   A container for storing data , It holds a series of organized data .
• DBMS： Database management system （DataBase Management System） Also known as database software or database products , Used to create or manage DB.
• SQL： Structured query language （Structure Query Language） The language used to communicate with the database , It's not unique to any database software , It's almost all
• Common language of mainstream database software .

3. According to different data types, it can be divided into ：

Relational database ：

• A relational database management system is called RDBMS,R finger Relation
• Oracle: Powerful , charge .
• MySQL quick 、 reliable Open source 、 free
• SQL Server( Microsoft ): Can only be installed in Windows operating system
• DB2 (IBM)

• MongdoDB
• Redis

• Case insensitive , It is suggested to capitalize the keywords , Table name 、 Column names in lowercase
• Use every word ;

• Single-line comments ：# Note text
• Single-line comments ：
• Note text （ There should be spaces ）
• Multiline comment ：
• /* Note text */

 DDL

● data ( structure ) Define language DDL(Data Definition Language), Is a language used to create and modify database table structure .

● Common sentences ：create ,alter,drop,rename

Create a database and set the encoding format

CREATE DATABASE [if not exists] Database name [ CHARSET utf8]

  Delete database

DROP DATABASE Database name / [IF EXISTS Database name ];

Modify character set

ALTER DATABASE Database name CHARSET gbk;

• Put the data in the table , Put the watch in the library
• There can be multiple tables in a database , Every watch has a name , To identify yourself . Table names are unique .
• Table has some characteristics , These properties define how data is stored in tables , similar Java in “ class ” The design of the .
• Table consists of columns , We also call columns fields . All tables are made up of one or more columns , Each column is similar to java Medium ” attribute ”
• The data in the table is stored by row , Each line is similar to Java Medium “ object ”.

Design table data type  

• char（n） The length is n Fixed length string
• varchar(n） Maximum length is n Variable length string
• date date ,
• Including mm / DD / yyyy
• datetime Specific date Minutes and seconds

Delete table

DROP TABLE [if exists ] Table name

Modify the name of the table

RENAME TABLE The old name of the table TO The new name of the table

Replicated table structure

CREATE TABLE The new name of the table LIKE Copied table name ;

insert data

The way 1: INSERT INTO Table name ( Column 1, Column 2……, Column n) VALUES( value 1, value 2….., value n);

The way 2: INSERT INTO Table name set Name 1= value 1,.. Name n= value n;

The way 3: INSERT INTO Table name ( Column 1, Column 2……, Column n) VALUES( value 1, value 2….., value n),( value 1, value 2….., value n);

The way 4:INSERT INTO Table name ( Column 1, Column 2……, Column n) Query statement ( The number of columns queried matches the number of inserted columns )

Modifying data

UPDATE Table name SET Name = ‘ The new value ’WHERE Conditions

Delete data

DELETE FROM Table name WHERE Conditions

TRUNCATE TABLE Table name ; Clear the whole table

A little practice ： 

CREATE DATABASE baseketballteam;
CREATE TABLE basketball(
 Team number  INT PRIMARY KEY,
 Team name  VARCHAR(5),
 home   VARCHAR(5)
)

CREATE TABLE basketmember(
 Number  INT PRIMARY KEY AUTO_INCREMENT,
 name  VARCHAR(10),
 Birthday  DATE,
 height  DOUBLE(3,2) CHECK( height >1.8),
 weight  INT,
 Location  VARCHAR(5)
)

 #drop table basketmember
INSERT INTO basketmember( name , Birthday , height , weight , Location )
VALUES(' Dwayne . wade ','1982-1-17',1.93,96,'null'),
      (' lebron . James ','1984-12-30',2.03,113,' striker '),
      (' Kobe . Bryant ','1978-8-23',1.92,99,' defender '),
      (' Deco . Dirk Nowitzki ','1978-6-19',2.13,111,'null'),
      (' Iris . Paul ','1985-5-6',1.82,79,' defender '),
      (' Tony . Parke ','1982-5-17',1.87,83,' defender '),
      (' Kevin . Garnett ','1981-7-14',2.12,113,'null'),
      (' Paul . Pierce ','1977-10-13',2.00,106,' striker '),
      (' Michael . Jordan ','1963-2-17',1.98,98,' striker '),
      (' Dwight - Howard ','1985-12-18',2.10,120,' Center-forward '),
      (' Yao Ming ','1980-9-12',2.29,140,' Center-forward '),
      (' Shaquille . O'Neill ','1972-3-6',2.15,147,' Center-forward ')  
      
       UPDATE basketmember SET  Location =' Center-forward ' WHERE  Number =1
      
      DELETE FROM basketmember WHERE  Number =12