MySQL | basic commands

1. Operating the database

1. Create database CREAT DATABASE [IF NOT EXISTS] name [] With or without
2. Delete database DROP DATABASE [IF EXISTS] name
3. Using a database use name
4. view the database show DATABASE

2. Properties of fields

ZEROFILL: use 0 Filled with , The number of missing digits is 0 Fill in

Auto_InCrement: Self increasing , Default Auto +1, Usually used to design primary keys , You can set the starting value and the length of one increase by yourself :

• Current table setting step (AUTO_INCREMENT=100) : Only the current table
• SET @@auto_increment_increment=5 ; Affect all tables using auto increment ( overall situation )

NOT NULL: The column must have a value

DEFAULT: The default value is

Example

CREATE TABLE IF NOT EXISTS `user`(
	`id` INT(4) NOT NULL AUTO_INCREMENT COMMENT ' Add notes , This is the user id',
	`name` VARCHAR(30) NOT NULL  COMMENT ' user name ',
	`pwd` VARCHAR(30) NOT NULL COMMENT ' password '
	PRIMARY KEY (`id`)
)ENGINE = INNODB
	

modify the database

Modify the name of the table :ALTER TABLE The old name of the table RENAME AS The new name of the table

Add fields ( attribute ): ALTER TABLE Table name ADD Field name attribute A field is a column of a table

Modify fields :

• ALTER TABLE Table name MODIFY Field name attribute
• ALTER TABLE Table name CHANGE Old field name new field name attribute ( Used to modify column names )

Delete field :ALTER TABLE Table name DROP Field name

Delete table :DROP TABLE [IF EXISTS] Table name

Add or delete check change

insert

INSERT INTO `user`(`pwd`) VALUES ('123');// Insert... For a single attribute 

INSERT INTO `user`(`id`,`name`,`pwd`) VALUES ('3','FXL','564123'),('4','KKK','123456');// Insert multiple data 

INSERT INTO `user` VALUES ('3','FXL','564123');// Omit field insertion , The premise is that all fields are satisfied . One-to-one correspondence 

update

UPDATE `user` SET `id`='6' WHERE `name`= 'FXL';// Specified conditions 

When not specified , All lines will be changed

delete

// Delete all 
DELETE FROM `user`;
// Delete specified data 
DELETE FROM `user` WHERE `id`=1;

DELETE and TRUNCATE The difference between ：

DELETE You can conditionally delete （where Clause ）, and TRUNCATE Only the entire table can be deleted
TRUNCATE Reset auto increment column , The counter will go to zero , and DELETE It won't affect self growth
DELETE Data manipulation language （DML - Data Manipulation Language）, During operation, the original data will be put into rollback segment in , Can be rolled back ; and TRUNCATE It's data definition language （DDL - Data Definition Language), Operation will not be stored , Cannot roll back .