Database: MySQL foundation +crud basic operation

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1.MySQL Basics

Configure environment variables

// stay path Add MySQL The global path of can be in cmd Use in ;

// Use ：mysql -u rooy -p + password ;
// Exit database ： quit;

// After installation and configuration , Enter the password at the customer service end , The following conditions indicate no abnormal conditions ：

DDL 、DML、DCL

• DDL Data definition language , Used to maintain the structure of stored data （ For instructions : create, drop, alter）;
• DML Data manipulation language , Used to manipulate data （ For instructions ： insert,delete,update,（DQL Instructions select））;
• DCL Data control language , Mainly responsible for authority management and affairs （ For instructions ：grant,revoke,commit）

Basic operation

// Display database 、 Create database 、 Using a database 、 Delete database

	show databases;
	create database if not exists data0;
	create database data1 character set utf8mb4;
	use data01;
	drop database if exists data01;

data type

value type

Character type

Date or time type

2.CRUD Basic operation

* newly added (create)

Table operations

// Common tables 、 View table structure 、 Delete table 、 Show all tables ;
// You must use+ Database name Using a database ;

	use data0;
	create table if not exists exam(
		id int,
		name varchar(20),
		chinses decimal(3,1),
		math decimal(3,1),
		english decimal(3,1)
	);
	show tables;
	desc exam;
	drop table if exists exam;

insert data

• Single line input 、 Multi line input

	INSERT INTO student VALUES (100, 10000, ' Tang Sanzang ', NULL);
	insert into exam value(id,name,chinese,math,english) values
	    (1,' Tang Sanzang ', 67, 98, 56),
	    (2,' The Monkey King ',87.5, 78,77),
	    (3,' Pig Wuneng ',88, 98.5,98),
	    (4,' Cao mengde ',82,84,67),
	    (5,' Liu Xuande ',55.5,85,45),
	    (6,' king of Wu in the Three Kingdoms Era ',70,73,78.5),
	    (7,' Song Gongming ',75,65,30);

* Inquire about （Retrieve)

Column query 、 duplicate removal distinct、 Field expression query

// Full column query （ * Inquire about All column data in this table ）

// Individual column query

// The query field can be an expression

// Query fields can be aliased : Original name [AS] Alias ;

// Use distinct Keyword de duplication

	select distinct english from exam;

// Sort order by（NULL Data is the smallest by default ）

-- ASC  In ascending order （ From small to large ）
-- DESC  For the descending order （ From big to small ）
--  The default is  ASC
    SELECT ... FROM table_name [WHERE ...]
        ORDER BY column [ASC|DESC], [...];

Conditions of the query where

1. WHERE Conditions can be expressed as , But you can't use aliases .
2. AND Has a higher priority than OR, When used at the same time , You need to use parentheses () The priority part of the package

Paging query LIMIT

// Often with ORDER BY Continuous use

• LIMIT n —— Indicates from subscript 0 Start screening n Results ;
• LIMIT s,n —— Indicates from the following table as s Start screening n results ;
• LIMIT n OFFSET s —— From s Start , Screening n results （ If the data ends , The screening is not over , Does not affect the ）;
  

* modify （Update）

	UPDATE table_name SET column = expr [, column = expr ...]
 		[WHERE ...] [ORDER BY ...] [LIMIT ...];

* Delete （Delete）

	DELETE FROM  table_name [WHERE ...] [ORDER BY ...] [LIMIT ...];

// Delete a column in a table

	alter table  Table name  drop  Name ;

// Delete all values in a table

	delete from  Table name ;

// Delete the values of all fields in a table

	update  Table name  SET  Name  = '';

// Delete a table

	drop table  Table name ;

// Delete a database

	drop database  Database name ;