MySQL learning notes

To be improved after the re examination

 

Basic concepts of database

1.  English words in the database ： DataBase  abbreviation  ： DB
2.  What database ？
	*  A warehouse for storing and managing data .

3.  The characteristics of database ：
	1.  Persistent storage of data . In fact, the database is a file system 
	2.  Easy to store and manage data 
	3.  Using a unified way to operate the database  -- SQL

MySQL Database software

1.  install 
	*  See 《MySQL Basics .pdf》
2.  uninstall 
	1.  Go to mysql The installation directory is found my.ini file 
		*  Copy  datadir="C:/ProgramData/MySQL/MySQL Server 5.5/Data/"
	2.  uninstall MySQL
	3.  Delete C:/ProgramData In the catalog MySQL Folder .
	
3.  To configure 
	* MySQL Service startup 
		1.  Manual .
		2. cmd--> services.msc  Open the service window 
		3.  Use the administrator to open cmd
			* net start mysql :  start-up mysql Service for 
			* net stop mysql: close mysql service 
	* MySQL Sign in 
		1. mysql -uroot -p password 
		2. mysql -hip -uroot -p Password to connect to target 
		3. mysql --host=ip --user=root --password= Password to connect to target 
	* MySQL sign out 
		1. exit
		2. quit

	* MySQL Directory structure 
		1. MySQL The installation directory ：basedir="D:/develop/MySQL/"
			*  The configuration file  my.ini
		2. MySQL Data directory ：datadir="C:/ProgramData/MySQL/MySQL Server 5.5/Data/"
			*  Several concepts 
				*  database ： Folder 
				*  surface ： file 
				*  data ： data 

SQL

1. What is? SQL？
	Structured Query Language： Structured query language 
	 In fact, it defines the rules for operating all relational databases . There are different ways of database operation , be called “ dialect ”.
	
2.SQL General grammar 
	1. SQL  Statements can be written in one or more lines , It ends with a semicolon .
	2.  You can use spaces and indents to enhance the readability of statements .
	3. MySQL  Database  SQL  Statement is case insensitive , It is recommended to use uppercase .
	4. 3  Species notes 
		*  Single-line comments : --  The comment   or  #  The comment (mysql  specific ) 
		*  Multiline comment : /*  notes  */
	
3. SQL classification 
	1) DDL(Data Definition Language) Data definition language 
		 Used to define database objects ： database , surface , Column, etc. . keyword ：create, drop,alter  etc. 
	2) DML(Data Manipulation Language) Data operation language 
		 It is used to add, delete and modify the data in the database . keyword ：insert, delete, update  etc. 
	3) DQL(Data Query Language) Data query language 
		 Used to query the records of tables in the database ( data ). keyword ：select, where  etc. 
	4) DCL(Data Control Language) Data control language ( understand )
		 It is used to define the access rights and security level of the database , And create users . keyword ：GRANT, REVOKE  etc. 

DDL: Operating the database 、 surface

1.  Operating the database ：CRUD
	1. C(Create): establish 
		*  Create database ：
			* create database  Database name ;
		*  Create database , Judgment does not exist , To create a ：
			* create database if not exists  Database name ;
		*  Create database , And specify the character set 
			* create database  Database name  character set  Character set name ;

		*  practice ：  establish db4 database , Judge whether it exists , And make character set as gbk
			* create database if not exists db4 character set gbk;
	2. R(Retrieve)： Inquire about 
		*  Query all database names :
			* show databases;
		*  Query the character set of a database : Query the creation statement of a database 
			* show create database  Database name ;
	3. U(Update): modify 
		*  Modify the character set of the database 
			* alter database  Database name  character set  Character set name ;
	4. D(Delete): Delete 
		*  Delete database 
			* drop database  Database name ;
		*  Determine that the database exists , Exist and delete 
			* drop database if exists  Database name ;
	5.  Using a database 
		*  Query the database name currently in use 
			* select database();
		*  Using a database 
			* use  Database name ;


2.  Operation table 
	1. C(Create): establish 
		1.  grammar ：
			create table  Table name (
				 Name 1  data type 1,
				 Name 2  data type 2,
				....
				 Name n  data type n
			);
			*  Be careful ： The last column , There is no need to add comma （,）
			*  Database type ：
				1. int： Integer types 
					* age int,
				2. double: Decimal type 
					* score double(5,2)
				3. date: date , Include only mm / DD / yyyy ,yyyy-MM-dd
				4. datetime: date , Including month, day, hour, minute, second 	 yyyy-MM-dd HH:mm:ss
				5. timestamp: Wrong type of time 	 Including month, day, hour, minute, second 	 yyyy-MM-dd HH:mm:ss	
					*  If you don't assign a value to this field in the future , Or assign the value to null, The current system time is used by default , To automatically assign 

				6. varchar： character string 
					* name varchar(20): The biggest name 20 Characters 
					* zhangsan 8 Characters    Zhang San  2 Characters 
			

		*  Create table 
			create table student(
				id int,
				name varchar(32),
				age int ,
				score double(4,1),
				birthday date,
				insert_time timestamp
			);
		*  Copy table ：
			* create table  Table name  like  The name of the copied table ;	  	
	2. R(Retrieve)： Inquire about 
		*  Query all table names in a database 
			* show tables;
		*  Query table structure 
			* desc  Table name ;
	3. U(Update): modify 
		1.  Modify the name of the table 
			alter table  Table name  rename to  New table name ;
		2.  Modify the character set of the table 
			alter table  Table name  character set  Character set name ;
		3.  Add a column 
			alter table  Table name  add  Name   data type ;
		4.  Change column name   type 
			alter table  Table name  change  Name   New listing   New data types ;
			alter table  Table name  modify  Name   New data types ;
		5.  Delete column 
			alter table  Table name  drop  Name ;
	4. D(Delete): Delete 
		* drop table  Table name ;
		* drop table  if exists  Table name  ;

SQLYog Installation and use :

Reference blog ：

sqlyog Installation details

SQLyog An error occurred when connecting to the database plugin caching_sha2_password could not be loaded

DML： Add, delete and modify the data in the table

1.  Add data ：
	*  grammar ：
		* insert into  Table name ( Name 1, Name 2,... Name n) values( value 1, value 2,... value n);
	*  Be careful ：
		1.  Column name and value should correspond one by one .
		2.  If the name comes after , No column name defined , The default is to add values to all columns 
			insert into  Table name  values( value 1, value 2,... value n);
		3.  Except for the number type , Other types require quotation marks ( Single and double can ) Lead up 
2.  Delete data ：
	*  grammar ：
		* delete from  Table name  [where  Conditions ]
	*  Be careful ：
		1.  If there is no condition , Then delete all records in the table .
		2.  If you want to delete all records 
			1. delete from  Table name ; --  It is not recommended to use . How many records will be deleted 
			2. TRUNCATE TABLE  Table name ; --  Recommended , More efficient   Delete the table first , Then create the same table .
3.  Modifying data ：
	*  grammar ：
		* update  Table name  set  Name 1 =  value 1,  Name 2 =  value 2,... [where  Conditions ];

	*  Be careful ：
		1.  Without any conditions , All records in the table will be modified .

DQL： Look up the records in the table

* select * from  Table name ;

1.  grammar ：
	select
		 Field list 
	from
		 List of table names 
	where
		 List of conditions 
	group by
		 Grouping field 
	having
		 Conditions after grouping 
	order by
		 Sort 
	limit
		 Paging limit 


2.  Basic query 
	1.  Multiple field queries 
		select  Field name 1, Field name 2... from  Table name ;
		*  Be careful ：
			*  If you query all fields , You can use * To replace the field list .
	2.  Remove duplication ：
		* distinct
	3.  Calculated column 
		*  Generally, four operations can be used to calculate the values of some columns .（ Generally, only numerical calculation will be carried out ）
		* ifnull( expression 1, expression 2)：null Operations involved , The results are null
			*  expression 1： Which field needs to determine whether it is null
			*  If the field is null The replacement value after .
	4.  names ：
		* as：as You can omit it 
		

3.  Conditions of the query 
	1. where Clause followed by condition 
	2.  Operator 
		* > 、< 、<= 、>= 、= 、<>
		* BETWEEN...AND  
		* IN(  aggregate ) 
		* LIKE： Fuzzy query 
			*  Place holder ：
				* _: Any single character 
				* %： More than one arbitrary character 
		* IS NULL  
		* and   or  &&
		* or   or  || 
		* not   or  !
		
			--  Query age is greater than 20 year 

			SELECT * FROM student WHERE age > 20;
			
			SELECT * FROM student WHERE age >= 20;
			
			--  Query age = 20 year 
			SELECT * FROM student WHERE age = 20;
			
			--  Inquiry age is not equal to 20 year 
			SELECT * FROM student WHERE age != 20;
			SELECT * FROM student WHERE age <> 20;
			
			--  Query age is greater than or equal to 20  Less than or equal to 30
			
			SELECT * FROM student WHERE age >= 20 &&  age <=30;
			SELECT * FROM student WHERE age >= 20 AND  age <=30;
			SELECT * FROM student WHERE age BETWEEN 20 AND 30;
			
			--  Check age 22 year ,18 year ,25 Age information 
			SELECT * FROM student WHERE age = 22 OR age = 18 OR age = 25
			SELECT * FROM student WHERE age IN (22,18,25);
			
			--  The English score is null
			SELECT * FROM student WHERE english = NULL; --  It's not right .null Value cannot be used  = （!=）  Judge 
			
			SELECT * FROM student WHERE english IS NULL;
			
			--  The English score is not null
			SELECT * FROM student WHERE english  IS NOT NULL;



			--  Find out what's the name of Ma ？ like
			SELECT * FROM student WHERE NAME LIKE ' Horse %';
			--  The second word for a name is the person who changed 
			
			SELECT * FROM student WHERE NAME LIKE "_ turn %";
			
			--  The search name is 3 One word man 
			SELECT * FROM student WHERE NAME LIKE '___';
			
			
			--  Search for the person whose name contains De 
			SELECT * FROM student WHERE NAME LIKE '% Virtue %';