MySQL must master 4 languages!

This article mainly introduces to you MySQL Commonly used 4 Languages ：

One 、DDL

DDL,data defination language, refer to Data definition language , Its main function is to create a database , Delete and modify the structure of the library table .

Access to database

mysql -uroot -p    --  In this way , Next you need to enter the password . Password is secret 
mysql -uroot -p123456  --  The password can be directly 123456 Put it in the parameter p Behind , unsafe 

Parameter interpretation ：

• u： Designated user

• p： Specified password

  

  ---

All orders

1.  Database operation 
show databases;     //  Show all databases 
use school;     //  Use school database 
create database school;  //  Create database 
drop database school;  //  Delete a database 

2.  Table operations 
--  Create table 
create table user( Field 1, Field 2,..., Field n);   

--  View the SQL sentence 
show create table user;

--  View the structure of the table 
desc user;

--  Delete table 
drop table user;

--  Modify the name of the table 
alter table user rename to users;

Database operation

show databases;     //  Show all databases 
use school;     //  Use school database 
create database school;  //  Create database 
drop database school;  //  Delete a database 
mysql> show databases;   //  Display database 
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| peter              |
| school             |
| sys                |
+--------------------+
6 rows in set (0.04 sec)

mysql> use school;   //  Choose to use the database 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Table operations

// 1、 Create table 
create table user( Field 1,
                   Field 2, 
                  ..., 
                   Field n
                  );    //  The last semicolon must not be forgotten 
                  
// 2、 Look at all the tables 
show tables;

// 3、 View the structure of the table 
desc user;

// 4、 View the SQL sentence 
show create table user;

// 5、 Delete table 
drop table user;

// 6、 Modify the name of the table 
alter table user rename to users;   #  Change table name to users;to Omission 

• The last semicolon must not be forgotten

mysql> use school;  //  Use a database 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show tables;  //   Look at all the tables in the database 
+------------------+
| Tables_in_school |
+------------------+
| course           |
| score            |
| student          |
| teacher          |
| total            |
+------------------+
5 rows in set (0.00 sec)

Create table

• Primary key primary key  and auto_increment Must be used together

• Writing norms ： The statement of each field should be written separately , Easy to check

• The last semicolon must not be forgotten

#  establish user surface ：6 Species field +1 Primary keys 

create table user( id int(10) unsigned not null auto_increment comment "user_id",   // take id A primary key 
                  name varchar(20) not null comment "user_name", 
                  email varchar(50) not null comment "user_email", 
                  age tinyint unsigned not null comment "user_age", 
                  fee decimal(10,2) not null default 0.00 comment "user_fee", 
                  createTime timestamp not null comment "user_time", 
                  primary key(id)  
                 );    //  Remember the semicolon 

View table structure

mysql> desc user;
+------------+---------------------+------+-----+-------------------+-----------------------------+
| Field      | Type                | Null | Key | Default           | Extra                       |
+------------+---------------------+------+-----+-------------------+-----------------------------+
| id         | int(10) unsigned    | NO   | PRI | NULL              | auto_increment              |
| name       | varchar(20)         | NO   |     | NULL              |                             |
| email      | varchar(50)         | NO   |     | NULL              |                             |
| age        | tinyint(3) unsigned | NO   |     | NULL              |                             |
| fee        | decimal(10,2)       | NO   |     | 0.00              |                             |
| createTime | timestamp           | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+------------+---------------------+------+-----+-------------------+-----------------------------+
6 rows in set (0.02 sec)

View the SQL sentence

show create table user;

Field operations

The key word is alter, First select the table to be operated .

• modify： modify

• change： Change the name

• add： Add fields

  • The default is the end

  • Add... At the specified location

//  Modify field information 
alter table user modify name varchar(50) not null;   #  Change the field name  from 20 Change it to 50 Characters 

//  Modify field name 
alter table user change email user_email varchar(50) not null;  #  take email Change to user_email

//  Add a field at the end 
alter table user add password char(30) not null comment "user_password";   #  increase password Field 

//  Specify the location to add the field 
alter table user add password1 char(30) not null comment "user_password1" after user_name;   #  stay name Add... To the back password1 Field 

//  Delete field 
alter table user drop password1;        # Delete field password1
//  The original table information 

mysql> desc user;
+------------+---------------------+------+-----+-------------------+-----------------------------+
| Field      | Type                | Null | Key | Default           | Extra                       |
+------------+---------------------+------+-----+-------------------+-----------------------------+
| id         | int(10) unsigned    | NO   | PRI | NULL              | auto_increment              |
| name       | varchar(20)         | NO   |     | NULL              |                             |
| email      | varchar(50)         | NO   |     | NULL              |                             |
| age        | tinyint(3) unsigned | NO   |     | NULL              |                             |
| fee        | decimal(10,2)       | NO   |     | 0.00              |                             |
| createTime | timestamp           | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+------------+---------------------+------+-----+-------------------+-----------------------------+
6 rows in set (0.00 sec)

#  Modify field information 
mysql> alter table user modify name varchar(50); 
#  Modify field name 
mysql> alter table user change email user_email varchar(50) not null;
#  Add fields , At the end of 
mysql> alter table user add password char(30) not null comment "user_password";
#  Specify the location to add the field 
mysql> alter table user add password1 char(30) not null comment "user_password1" after name;

mysql> desc user;
+------------+---------------------+------+-----+-------------------+-----------------------------+
| Field      | Type                | Null | Key | Default           | Extra                       |
+------------+---------------------+------+-----+-------------------+-----------------------------+
| id         | int(10) unsigned    | NO   | PRI | NULL              | auto_increment              |
| name       | varchar(50)         | YES  |     | NULL              |                             |
| password1  | char(30)            | NO   |     | NULL              |                             |
| user_email | varchar(50)         | NO   |     | NULL              |                             |
| age        | tinyint(3) unsigned | NO   |     | NULL              |                             |
| fee        | decimal(10,2)       | NO   |     | 0.00              |                             |
| createTime | timestamp           | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| password   | char(30)            | NO   |     | NULL              |                             |
+------------+---------------------+------+-----+-------------------+-----------------------------+
8 rows in set (0.00 sec)

Two 、DML

DML,data manipulation language, refer to Data operation language . It is mainly the language for operating the table records in the database , Contains inserting data into the table 、 Update of data in the table 、 Deletion of tables, etc

• Insert data into the table

• The data in the table is updated

• Delete table

Insert data into the table

--  Match the field name to the field value one by one , You can just insert some fields 
--  omitted id and createtime Field 
mysql> insert into user(
            name, 
            email, 
            age, 
            fee, 
            password) 
values("xiaoming", 
           "[email protected]", 
           20, 
           56.56, 
           Password("xiaoming")     //  Password here to use the function Password()
      );
--  Contains all field information 
insert into user values(10, "nanan", "[email protected]", 38, 89.19, 2019-10-02, Password("nanan"));

• String fields must be enclosed in quotation marks

• The password requires the use of a function Password()

• Add a semicolon at the end of the statement

• Use insert only partial fields

• You can leave out the field name , At this point, we need to add id, And you have to fill in all the fields , You can't just add some data

Data update

Data update update The most used is where sentence , Specify a condition to execute ; If not where, All fields will be changed （ Be careful ）

• Appoint id Number

• Specify the specific value of the field

• Multiple fields are allowed , Separated by commas

mysql> update user set name="nangying" where id=6;   //  adopt id Appoint 
mysql> update user set fee=88.76 where fee=56.90;   //  Specify directly by field name 
mysql> update user set email="[email protected]", age=54 where id=7;  //  Modify multiple values at the same time 
mysql> update user set fee=88.88 where id in(2,4,6);   // in Usage of 
mysql> update user set fee=66.66 where id between 2 and 6;  // between ... and ...

Delete

There are two ways to delete a table ：

• delete： Delete table , insert data From the last time Of id We're going to start inserting ; Deleted records still exist

• truncate： Clear the table , Reinsert data id from 1 Start ; No memory space

delete table user;     
truncate table user;

• Delete delete A record in a table

delete from user where id=7;   //  Delete record 
insert into user (name,email,age,fee,password) values("lisi","[email protected]", 36, 81.17, Password("lisi"));  // id Is to increase from the original basis 

About truncate

#  Delete data 
mysql> truncate table user;
Query OK, 0 rows affected (0.05 sec)

mysql> select * from user;
Empty set (0.00 sec)

#  Reinsert data 
mysql> insert into user (user_name, user_email, user_age, password, fee) values ("peter", "[email protected]", 27, password("101010"), 28.87);
Query OK, 1 row affected, 2 warnings (0.01 sec)

mysql> select * from user;
+----+-----------+-----------------+----------+--------------------------------+-------+
| id | user_name | user_email      | user_age | password                       | fee   |
+----+-----------+-----------------+----------+--------------------------------+-------+
|  1 | peter     | [email protected] |       27 | *C3BC3E91915DCAE22014892F9827D | 28.87 |
+----+-----------+-----------------+----------+--------------------------------+-------+
1 row in set (0.00 sec)

3、 ... and 、DCL

data control language,DCL, It refers to data control language , It is mainly a language to control the login in the database and the user's permission , contain

• The user login MySQL database

• How to change the user password and forget the password

• Create common users and authorizations

• Revoke authority revoke

• View permissions and delete users

All orders

1.  View users and information in the database 
mysql -uroot -p
show databases;
use mysql;
show tables;
select user, host, passord from user;    #  All the users are user In the table 

2.  Create a new user 、 to grant authorization 、 Revoke permissions and delete 
--  establish 
create user "test"@"192.168.2.10" identified by"password";    #  Designated user test、ip And password password
flush privileges;  #  Refresh the permissions 
mysql -utest -h192.168.2.10 -p  #  use test The user login 

--  to grant authorization 
grant select, insert, delete on shop.* to "test"@"192.168.2.10";   # shop  It's the database ,test Is the table in the database 
flush privileges;  #  Refresh the permissions 
systemctl restart mysql;  #  restart mysql

--  Authorization while creating users 
grant select, insert, delete on shop.* to "test"@"192.168.2.10" identified  by"password";

--  View permissions 
show grants for "test"@"192.168.2.10"\G   # \G Parameters are used to output good-looking 

--  Revoke authority 
revoke delete on shop.* to "test"@"192.168.2.10";   #  revoke shop In the database test User delete jurisdiction 
flush privileges;  #  Refresh the permissions 
systemctl restart mysql;  #  restart mysql

--  Delete user 
drop user "test"@"192.168.2.10";

--  Prudent operation 
grant all privileges on *.* to "test"@"192.168.2.10"  #  Give all permissions to all databases 


3.  Change user password 
--  The user's original password is known , Be able to log in 
mysql -uroot -p
show databases;
use mysql;
show tables;
select user, host, password from user;    #  All the users are user In the table 
update user set password=PASSWORD("123456admin") where user="test";  #  take test Change the user's password to 123456admin
flush privileges;

--  Forget the original password ： With the help of the jump permission table , Restart the daemons 
mysql skip-grant-tables  #  Jump permission table 
mysql  #  Re enter mysql
show databases;use mysql;show tables;
select user, host, password from user;    #  All the users are user In the table 
update user set password=PASSWORD("123456admin") where user="test";  #  take test Change the user's password to 123456admin
flush privileges;

4.  see mysql service 
-- window
 Go directly to the task manager 
-- linux
netstat -an   #  find 3306 port 

About root Account

By default ,MySQL Database means to allow root Account login and login on this computer .

• -uroot Express root Account

• -p Indicates that a password is required

• No, -h Indicates that the default is local localhost perhaps 127.0.0.1 Sign in

Log in to view your account

MySQL The service port number of the database is 3306, By means of mysql Database user View the login database user information in the table ：

mysql> show databases;  #  View all databases 
mysql> use mysql;   #  choice mysql database 
mysql> show tables;   #  Look up all the tables in the database 
mysql> select user, host from user;   #  Look at... In this table user and host Information 

Delete user

It should be noted that the permission must be refreshed after deleting a user ：

mysql> delete from user where host="%";   #  Delete host by % Users of 
Query OK, 1 row affected (0.01 sec)

mysql> flush privileges;  #  Refresh the permissions 
Query OK, 0 rows affected (0.00 sec)

Be careful ： When in actual development projects , The project and the database server are not in the same place , You can specify ip Connect to access

mysql> update user set host="192.168.1.10" where user="root";
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select user,host from user;

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

When to exit mysql Re enter , You need to specify the IP Address , It's the one set up above IP：

Password problem

1、 Change Password

You also need to enter mysql Database user In the table

mysql>update user set password=PASSWORD("admin")  where user="root";   #  take root The password of the account is changed to admin

mysql> flush privileges;   #  update operation 
Query OK, 0 rows affected (0.00 sec)

2、 Forget the password

• If you forget the password , You need to enter the configuration file

[email protected]:~$ vim /etc/mysql/mysql.conf.d/mysqld.cnf

• Find the in the figure below skip-grant-tables, Ahead of # Get rid of , Just uncomment ： Cancel authority authentication , Open a new process in the background to avoid secret entry MySQL

  

• restart MySQL service ：systemctl restart mysql

• adopt MySQL Go straight into ：

• Then follow the above steps to reset the password

mysql> show databases;
mysql> use mysql;
mysql> select user, password  from user;
#  Next, reset the password 

Four 、DQL

DQL（data query language）, refer to Data query language , The main function is to query the data in the database , It is also the most common and important function .

There are many ways to query ： The joint query 、 Group query 、 Inline query 、 Subquery etc. , just so so Limit the number of queries etc. , Here are some common queries

Format ：

select 
	column1,
	column2,...  #  Fields to query  
from table_name   #  Table name 
where  Conditions 

Simple query

select 
	name,
	age 
from user
where id=4;   
where id in(1,3,5,7);
where name = "xiaoming";

Filter query

The keywords for filtering queries are distinct, Remove duplicate values from the field

--  Filter duplicate fields 
select distinct(password) from user;     # password Is a duplicate 
select distinct password from user;   #  Brackets can be omitted 

Link query

The keyword of connection query is concat

• Directly use the default connection mode of the system , Connect the original fields with underscores

• Use concat...as...,as Later, I specify the new field name of the connection

• Queries with a join symbol concat_ws("+", Name 1, Name 2); among "+" Is to specify the connector

select concat(name, email) from user;          #  The result shows concat(name_email)
select concat(name, email) as nameEmail from user;  #  Use the new field name with nameEmail To express 

Fuzzy query

The key word of fuzzy query is like, Chinese translation into image ：

mysql> select user_name from student where user_name like "peter";    #  image peter
mysql> select user_name from student where user_name like "%e";      # % Express arbitrarily , Indicates the name with e ending 
mysql> select user_name from student where user_name like "%e%";    #  Indicates that the name contains e

Sort query

Ascending the records in the table asc Or descending order desc Permutation , The default is ascending asc, At the same time, we need to use order by keyword ：

• Ascending ：asc, By default

• Descending ：desc

select * from student order by user_age asc;   #  The ascending order of age 
select * from student order by user_age desc;  #  The descending order of age 

Aggregate functions

select count(*) from student;    #  General record 
select sum( Name ) from student;  #  The sum of the 
select avg( Name ) from student;   #  Average 
select max/min( Name ) from student;  #  Maximum / Small value 

Limit query results

To limit the number of queries, use limit keyword

• Use it directly limit

• Use limit ... offset ...： Specify where to start displaying , How many lines are displayed

• Abbreviation ：limit 5, 4： Says from the first 5 OK, let's start , Show 4 Row data

select name, age from user limit 5;    --  Display only 5 Row data 
select name, age from user limit 5 offset 4;   --  From 4（offset） Line start display 5(limit) Row data  
select name, age from user limit 4, 5 ;  --  The effect same as above ： Before the comma is offset The content of , After the comma is limit Content 

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