[MySQL from introduction to mastery] [advanced part] (III) creation of MySQL users_ Modification_ Delete and password settings

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1. Key points

This article will first focus on MySQL How to create users in the database , Modify the user , Delete users and set passwords .

2. Environmental Science

Environmental Science	edition
Red Hat	4.8.5-39
MySQL	5.7

1. View all users

stay MySQL In the database , User information is stored in mysql Database user In the table , Just query the table to get all users

select host,user from user;

Here is to root Users to query , among host Represents the host ：localhost Indicates that only local connections can be made （ Can't connect remotely ）, and % You can connect both locally and remotely .user Represents the user's account .

3. Create user

stay MySQL In the database , The official recommendation CREATE USER Statement to create a new user , stay MySQL Version removed PASSWORD Encryption method , Therefore, direct use is not recommended INSERT Statement direct operation MySQL Medium user Table to add users .
Use CREATE USER Statement to create a new user , Must have CREATE USER jurisdiction . Every time you add a user ,CREATE USER The statement will be in the mysql Database user Add a record to the table , But the newly created account does not have any permissions , If the added account already exists ,CREATE USER Statement will return an error .
CREATE USER The basic syntax of a sentence is as follows ：

CREATE USER  user name  [IDENTIFIED BY ' password '][, user name  [IDENTIFIED BY ' password ']]

1. The user name parameter indicates the account number of the new user , By the user （User） And the host name （Host） constitute , default Host yes %;
2. “[]” Said the optional , in other words , You can specify that users need password authentication when logging in , You can also not specify password authentication , In this way, users can log in directly , however , This method of not specifying a password is not secure , It is not recommended to use . If you specify a password value , You need to use IDENTIFIED BY Specify the plaintext password value .
3. CREATE USER Statement can create multiple users at the same time .
   give an example ：

 create user 'zhangsan' identified by 'Abc123456&';

The reason , The password setting is so complicated , Because MySQL The password verification rules set in the database are relatively strong . Otherwise, the following error will be reported ：

mysql> create user 'zhangsan' identified by 'abcd1234';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

To view the password verification rules, you can execute the following statements ：

SHOW VARIABLES LIKE 'validate_password%';

among ,
validate_password_number_count Specifies the length of the data in the password ,
validate_password_special_char_count Specifies the length of special characters in the password ,
validate_password_mixed_case_count Specifies the length of the uppercase and lowercase letters in the password .
validate_password_policy type

policy	explain
0 or LOW	Length（ Only the length is limited ）
1 or MEDIUM	Length; numeric, lowercase/uppercase, and special characters
2 or STRONG	Length; numeric, lowercase/uppercase, and special characters; dictionary file
If , To set a simpler policy, execute the following command ：

set global validate_password_policy=LOW

4. Modify the user （ Rarely used ）

It is seldom used to modify the user's functions , The modifying user here only modifies the user's account , It just needs to be modified user Just watch , The statement is simple update sentence . for example ： Original

UPDATE user set user='li4' WHERE user='lisi';

5. Delete user

stay MySQL In the database , The official recommendation DROP USER Statement to delete a user , This statement will not only delete user User information in the table , There will be other settings , After executing the order , The deleted user will not be able to log in again MySQL. Use DROP USER You must have the permission of this command to delete users .
DROP USER The basic syntax of a sentence is as follows ：

DROP USER  user name  [@  host ][, user name ].....

1. The user name parameter indicates that you want to delete the user's account , By the user （User） And the host name （Host） constitute ;
2. “[]” Said the optional ,
3. DROP USER Statement can create multiple users at the same time , Delete multiple users separated by commas .
   give an example ：

DROP USER 'li4'@'localhost';

6. User password settings

6.1. Use ALTER USER Command to change the current user password ：

Users can use ALTER Command to change your password , The following statement represents modifying the password of the current login user . The basic grammar is as follows ：

ALTER USER USER() IDENTIFIED BY 'new_password'; 

Use ALTER Order to modify zhangsan User's password , Change the password to "abc1234A%", The order is as follows ：

6.2. Use SET Statement to modify the current user password ：

Use root The user login MySQL after , have access to SET Statement to change the password , Specifically SQL The statement is as follows ：

SET PASSWORD='new_password';

This statement will automatically encrypt the password and then assign it to the current user .
Use SET Statement to modify zhangsan User's password , Change the password to "abc1234A%".

summary

This article introduces in detail in MySQL How to create users in , Delete the user and set the password .