MySQL Foundation

1. Database related concepts

1.1 Database concept ： Warehouse for storing and managing data , Data is organized and stored . database （DataBase, abbreviation DB） Is to store the data on the hard disk , It can achieve the effect of persistent storage .
1.2 Database management system ： Large software for managing databases （DataBase Management System, abbreviation DBMS）
explain ： After installing the database management system on the computer , You can create a database through the database management system to store data , You can also add, delete, modify and query the data in the database through the system . That's what we talk about MySQL The database is actually MySQL Database management system .

1.3 Common database management system

Oracle： A large database of charges ,Oracle  Products of the company 
MySQL：  Open source free small and medium-sized databases . later  Sun The company acquired  MySQL, and  Sun  The company was again  Oracle  Acquisition 
SQL Server：MicroSoft  A database of medium-sized companies that charge .C#、.net  Such language is often used 
PostgreSQL： Open source free small and medium-sized databases 
DB2：IBM  The company's large charging database products 
SQLite： Embedded micro database . Such as ： As  Android  Built in database 
MariaDB： Open source free small and medium-sized databases 

1.4 SQL

• english ：Structured Query Language, abbreviation SQL, Structured query language
• Programming language for operating relational databases
• Define a unified standard for operating all relational databases , have access to SQL Operate all relational database management systems , in the future If other database management systems are used in the work , Use the same SQL To operate .

2.MySQL

2.1 install A little ...
2.2 MySQL Data model
Relational database ：
A relational database is a database based on a relational model , In short , Relational database is made up of several pieces that can be connected with each other Two-dimensional table Composed database
Data model ：

Summary :

• MySQL You can create multiple databases in , Each database corresponds to a folder on disk
• Multiple tables can be created in each database , Each corresponds to a... On disk frm file
• Each table can store multiple pieces of data , The data will be stored on disk MYD In file

3.SQL

• english ：Structured Query Language, abbreviation SQL
• Structured query language , A programming language for operating relational databases
• Define a unified standard for operating all relational databases
• For the same need , There may be some differences in each way of database operation , We call it “ dialect ”

DDL(Data Definition Language) ： Data definition language , Used to define database objects ： database , surface , Column, etc.
DDL Simple understanding is used to operate the database , Table, etc

DML(Data Manipulation Language) Data operation language , It is used to add, delete and modify the data in the database
DML Simply understand and add, delete and modify the data in the table .

DQL(Data Query Language) Data query language , Used to query the records of tables in the database ( data )
DQL The simple understanding is to query the data . Query the data we want from the database table .

DCL(Data Control Language) Data control language , It is used to define the access rights and security level of the database , And create users
DML The simple understanding is to control the permissions of the database . For example, I let a database table be operated by only one user .

Be careful ： The most common thing we will do in the future is DML and DQL , Because the most common operation in our development is data .

DDL

1. Operating the database

1. Query all databases 
SHOW DATABASES;
2. Create database 
CREATE DATABASE  Database name ;
3. Delete database 
DROP DATABASE  Database name ;
4. Using a database 
USE  Database name ;
5. View currently used databases 
SELECT DATABASE();

2. Operation data sheet

1. Query the names of all tables in the current database 
SHOW TABLES;
2. Query table structure 
DESC  The name of the table ;
3. Create table 
CREATE TABLE  Table name  (
	 Field name 1   data type 1,
	 Field name 2   data type 2,
	…
	 Field name n   data type n
);
4. Delete table 
DROP TABLE  Table name ;
5. Modify the name of the table 
ALTER TABLE  Table name  RENAME TO  New table name ;
6. Add a column 
ALTER TABLE  Table name  ADD  Name   data type ;
7. Change data type 
ALTER TABLE  Table name  MODIFY  Name   New data types ;
8. Change column name and data type 
ALTER TABLE  Table name  CHANGE  Name   New column names   New data types ;
9. Delete column 
ALTER TABLE  Table name  DROP  Name ;

DML

DML It mainly increases the data （insert） Delete （delete） Change （update） operation .

1. Add data 
1.1 Add data to the specified column 
INSERT INTO  Table name ( Name 1, Name 2,…) VALUES( value 1, value 2,…);
1.2 Add data to all columns 
INSERT INTO  Table name  VALUES( value 1, value 2,…);
1.3 Batch add data 
INSERT INTO  Table name ( Name 1, Name 2,…) VALUES( value 1, value 2,…),( value 1, value 2,…),( value 1, value 2,…)…;


2. Modifying data 
2.1 Modify table data 
UPDATE  Table name  SET  Name 1= value 1, Name 2= value 2,… [WHERE  Conditions ] ;

3.  Delete data 
3.1 Delete data 
DELETE FROM  Table name  [WHERE  Conditions ] ;

DQL

SELECT 
     Field list 
FROM 
     List of table names  
WHERE 
     List of conditions 
GROUP BY
     Grouping field 
HAVING
     Conditions after grouping 
ORDER BY
     Sort field 
LIMIT
     Paging limit