Various usages of MySQL backup database to create table select and how many days are left

Command line that must be remembered

mysql -u root -p

mysql -h  Host name （192.168.200.1） Fill in the host name you want to link  -P 3306 Port number  -p

 Input password 

Accuracy in work use DOUBLE and DECIMAL Do not use float

Start the service

net start mysql

 Close the service 

net stop mysql

Backup database

stay dos（ No MYSQL Next ） To execute under orders -B Represents the entire table

mysqldump -u root -p -B db02 > d:\\bak.sql

mysqldump -u root -p  database  db02  surface 2 > d:\\bak.sql

Remember to take the path

Recover database （ When entering MYSQL Give orders ）

mysql -u -root -p

SOURCE d:\\bak.sql

Delete database

DROP DATABASE db02

Find database elements

SELECT * FROM users WHERE NAME=' Zhang San '

establish MySql surface （ Pay attention to the position of the table ）

CREATE TABLE `bobo`(
	id INT,
	`name` VARCHAR(255),
	`password` VARCHAR(255),
	`birthday` DATE)
	CHARACTER SET utf8 COLLATE utf8_bin ENGINE INNODB;

Create table emp,char There should be characters in it , The difference between characters and bytes

CREATE TABLE `emp`(
	id INT,
	`name` VARCHAR(32),
	sex CHAR(1),
	brithday DATE,
	entryday DATETIME,
	job CHAR(32),
	salary FLOAT,
	`resume` TEXT) CHARSET utf8 COLLATE utf8_bin ENGINE INNODB;

Write data to the table , Remember to add parameters （id,name,sex,date,datetime,zhiye,sarlary,resume）

INSERT INTO `emp` 
	VALUES('100',' Tang Bo ',' male ','1996-08-18','2019-11-11 11:12',' The programmer ','5000',
	' I am a bobo');

# increase image Column

# View table structure
DESC `emp`

modify job Table properties

# increase image Column 
ALTER TABLE `emp` ADD image VARCHAR(32) AFTER RESUME
# View table structure 
DESC `emp`

# modify job type  by  varchar(80) It is not empty by default 
ALTER TABLE emp
	MODIFY job VARCHAR(80) NOT NULL DEFAULT ''

Delete table attributes

ALTER TABLE emp
	DROP brithday;

Modify the name of the table

RENAME TABLE emp TO eeemmppp

Change column names

ALTER TABLE eeemmppp CHANGE `name`  `user_name` VARCHAR(50) NOT NULL DEFAULT ''

Update table data

UPDATE eeemmppp SET salary = '9000' WHERE id ='120'

Delete the old monster's record

DELETE FROM eemmpp
    WHERE user_name = ' Old monster ';

Various select usage

CREATE TABLE students(
	`id` INT NOT NULL DEFAULT 1,
	`name` VARCHAR(20) NOT NULL DEFAULT '',
	`chinese` FLOAT NOT NULL DEFAULT '0.0',
	`english` FLOAT NOT NULL DEFAULT '0.0',
	`match` FLOAT NOT NULL DEFAULT '0.0'
);
INSERT INTO students(id,`name`,chinese,english,`match`) VALUES ('1',' Tang Bo ','100','100','100'),
INSERT INTO students(id,`name`,chinese,english,`match`) VALUES ('2',' Zhang Bo ','12','102','104');

SELECT * FROM students
SELECT * FROM students WHERE chinese =100
SELECT `name`,english FROM students WHERE english = 100
SELECT DISTINCT english FROM students
SELECT `name`,(chinese+english+`match`) FROM students
SELECT `name`,(chinese+english+`match`+10) FROM students
SELECT `name` AS ` full name `,(chinese+english+`match`+10) AS total FROM students

How many days are left

SELECT * FROM students
	ORDER BY chinese
	
SELECT `name`,(chinese+english+`match`) AS total FROM students
	ORDER BY total DESC
	
SELECT COUNT(*) FROM students WHERE chinese = 100
SELECT COUNT(*) FROM students WHERE `match` > 100

SELECT SUM(english) FROM students
SELECT SUM(english) AS english,SUM(chinese) AS chinese,SUM(`match`) AS `match` FROM students

SELECT AVG(`match`) FROM students
SELECT AVG(`match`+english+chinese) FROM students

SELECT MAX(`chinese`) FROM students
SELECT MIN(`chinese`) FROM students

# a key 
SELECT AVG(`match`),MAX(english) FROM students GROUP BY chinese HAVING chinese > 20、

# How many days have I lived 
SELECT DATEDIFF('2021-09-11','1996-08-18') FROM DUAL
SELECT DATEDIFF(NOW(),'1996-08-18') FROM DUAL

# Live to 80 How many days are left in the year old 
SELECT DATEDIFF(DATE_ADD('1996-08-18',INTERVAL 80 YEAR),NOW()) FROM DUAL

Create index and query index (UNIQUE Both index and ordinary index can be used ）, Delete use DROP

SHOW TABLES
SELECT * FROM students

CREATE UNIQUE INDEX bobo ON students(`name`);

SHOW  UNIQUE INDEX FROM students

Show current database

# Display the current user and IP
SELECT USER() FROM DUAL

# Current database 
SELECT DATABASE() FROM DUAL

#MD5 encryption 
SELECT MD5(' Tang Bo 6768787') FROM DUAL

Capitalize to lowercase

SELECT CONCAT(LCASE(SUBSTRING(ename,1,1)), SUBSTRING(ename,2)) FROM emp

Display name without R Of Everyone's name

SELECT * FROM EMP 
        where ename not like "%R%"

Display the first three characters of the employee's name

select LEFT(ename,3)
        from emp

Write in all capitals A Replace with lowercase a

select replace(ename,"A","a") from emp

Working for more than ten years

select ename,hiredate
        from emp
        where DATE_ADD(hiredate,INTERVAL 10 YESR)< NOW()

Create a new user format

CREATE USER 'bobo2' @'localhost' IDENTIFIED BY '123456'

bobo2 Change your password set password=password('1234567')

root Changing Bobo's password can succeed

set password for 'bobo2' @ 'localhost'=password('1234567')

root User give bobo2 Permission to view the table

GRANT SELECT,INSERT
	ON db02.students 
	TO 'bobo2' @'localhost'

to bobo2 Modify the permissions

GRANT UPDATE,INSERT
	ON db02.students 
	TO 'bobo2' @'localhost'

To view the user

SELECT * FROM mysql.user