MySQL common basic commands

Database related operations

#  View all databases 
show databases;

#  Switch database 
use  Database name ;

#  Check the database currently in use 
select database();

#  Create database 
create database  Data name  charset=utf8;

#  Delete database 
drop database  Database name ;

Data table related operations

#  View all tables in the current database 
show tables;

#  View table structure 
desc  Table name ;

#  Create table 
'''
auto_increment Define properties that are listed as self incrementing , Generally used for primary key , The value will be added automatically 1.
 If you don't want the field to be  NULL  You can set the property of the field to  NOT NULL
PRIMARY KEY Keywords are used to define columns as primary keys .  You can use multiple columns to define the primary key , Columns are separated by commas 
'''

create table test_table(
    -> id int not null auto_increment,
    -> name varchar(15) not null,
    -> age int not null,
    -> address varchar(105),
    -> create_date date,
    -> primary key (id)
    -> );


#   Modify table  -  Add fields to the table :  If the field name is the same as that in the table, modify the field type 
## alter table  Table name  add  Field name   type ;
alter table test_mysql.test_table  add score int not null;

#  Modify table  -  Modify fields :  You cannot add fields to a table , Only existing field types can be modified 
## alter table  Table name  modify  Field name   New type ;
alter table test_mysql.test_table modify score decimal(3,1);

#  Modify table  -  Delete field 
## alter table  Table name  drop  Field name ;
alter table test_mysql.test_table drop address;

#  Delete table 
drop table  Table name ;

#  View the creation statement of the table 
show create table  Table name ;

increase 、 Delete 、 Change 、 check

#  Add data 
##  Add one piece of data at a time 
insert into test_table(id,name,age,create_date,score) values(1,' Xiao Ming ',18,now(),94.5);

##  Add more than one piece of data at a time （ above ID Set self growth , Add data below without manual setting ）
insert into test_table(name,age,create_date,score) values
    -> (' Xiaohong ',17,now(),99.4),
    -> (' Small blue ',18,now(),88.6),
    -> (' Little misery ',17,now(),66.3);



#  Query data 
##  Inquire about  ID == 1  A single piece of data , where  Followed by   Matching condition .
mysql> select * from test_table where id=1;
+----+--------+-----+-------------+-------+
| id | name   | age | create_date | score |
+----+--------+-----+-------------+-------+
|  1 |  Xiao Ming    |  18 | 2021-09-26  |  94.5 |
+----+--------+-----+-------------+-------+


##  Query all the data 
mysql> select * from test_table;
+----+--------+-----+-------------+-------+
| id | name   | age | create_date | score |
+----+--------+-----+-------------+-------+
|  1 |  Xiao Ming    |  18 | 2021-09-26  |  94.5 |
|  2 |  Xiaohong    |  17 | 2021-09-26  |  99.4 |
|  3 |  Small blue    |  18 | 2021-09-26  |  88.6 |
|  4 |  Little misery    |  17 | 2021-09-26  |  66.3 |
+----+--------+-----+-------------+-------+

#  Modifying data 
## update  Table name  set  Column 1= value 1, Column 2= value 2... where  Conditions 
update test_table set score=54.5 where name=' Little misery ';

#  Delete data 
## delete from  Table name  where  Conditions 
delete from test_table where id=4;

Sort 、 Aggregate functions

#  Sort 
## select * from  Table name  order by  Field name  asc|desc ...
##  Ann is arranged in ascending order 
mysql> select * from test_table order by score asc;
+----+--------+-----+-------------+-------+
| id | name   | age | create_date | score |
+----+--------+-----+-------------+-------+
|  3 |  Small blue    |  18 | 2021-09-26  |  88.6 |
|  1 |  Xiao Ming    |  18 | 2021-09-26  |  94.5 |
|  2 |  Xiaohong    |  17 | 2021-09-26  |  99.4 |
+----+--------+-----+-------------+-------+

##  Ann is arranged in descending order 
mysql> select * from test_table order by score desc;
+----+--------+-----+-------------+-------+
| id | name   | age | create_date | score |
+----+--------+-----+-------------+-------+
|  2 |  Xiaohong    |  17 | 2021-09-26  |  99.4 |
|  1 |  Xiao Ming    |  18 | 2021-09-26  |  94.5 |
|  3 |  Small blue    |  18 | 2021-09-26  |  88.6 |
+----+--------+-----+-------------+-------+


#  Aggregate functions  -  total 
## count (*)  To calculate the total number of lines , Write stars and column names in brackets , The result is the same 
mysql> select count(*) from test_table;
+----------+
| count(*) |
+----------+
|        3 |
+----------+

#  Aggregate functions  -  Maximum 
## max ( Column )  To find the maximum value of this column 
mysql> select max(score) from test_table;
+------------+
| max(score) |
+------------+
|       99.4 |
+------------+

#  Aggregate functions  -  minimum value 
## min ( Column )  To find the minimum value of this column 
mysql> select min(score) from test_table;
+------------+
| min(score) |
+------------+
|       88.6 |
+------------+

#  Aggregate functions  -  Sum up 
## sum ( Column )  Means to find the sum of this column 
mysql> select sum(score) from test_table;
+------------+
| sum(score) |
+------------+
|      282.5 |
+------------+

#  Aggregate functions  -  Average 
## avg ( Column )  Means to find the average value of this column 
mysql> select avg(score) from test_table;
+------------+
| avg(score) |
+------------+
|   94.16667 |
+------------+

grouping

#  preparation , Add data 
mysql> insert into test_table(name,age,create_date,score) values 
    -> (' Xiaohong ',17,now(),22.7),
    -> (' Xiaohong ',17,now(),88.2),
    -> (' Small blue ',18,now(),92.6),
    -> (' Small blue ',18,now(),66.6),
    -> (' Xiao Ming ',18,now(),92.6),
    -> (' Xiao Ming ',18,now(),33.3),
    -> (' Little misery ',18,now(),92.6);
#  Query data 
mysql> select * from test_table;
+----+--------+-----+-------------+-------+
| id | name   | age | create_date | score |
+----+--------+-----+-------------+-------+
|  1 |  Xiao Ming    |  18 | 2021-09-26  |  94.5 |
|  2 |  Xiaohong    |  17 | 2021-09-26  |  99.4 |
|  3 |  Small blue    |  18 | 2021-09-26  |  88.6 |
|  5 |  Xiaohong    |  17 | 2021-09-26  |  22.7 |
|  6 |  Xiaohong    |  17 | 2021-09-26  |  88.2 |
|  7 |  Small blue    |  18 | 2021-09-26  |  92.6 |
|  8 |  Small blue    |  18 | 2021-09-26  |  66.6 |
|  9 |  Xiao Ming    |  18 | 2021-09-26  |  92.6 |
| 10 |  Xiao Ming    |  18 | 2021-09-26  |  33.3 |
| 11 |  Little misery    |  18 | 2021-09-26  |  92.6 |
+----+--------+-----+-------------+-------+

#  grouping 
## group by, Query results according to  1  One or more fields to group , The fields with the same value are a set of . Can be used to group individual fields , It can also be used to group multiple fields 

##  Group according to a single field 
mysql> select name from  test_table group by name;
+--------+
| name   |
+--------+
|  Little misery    |
|  Xiao Ming    |
|  Xiaohong    |
|  Small blue    |
+--------+


# group by +  Set function 
##  Example ：  Group data tables by name , And count how many records each person has 
mysql> select name,count(*) from  test_table group by name;
+--------+----------+
| name   | count(*) |
+--------+----------+
|  Little misery    |        1 |
|  Xiao Ming    |        3 |
|  Xiaohong    |        3 |
|  Small blue    |        3 |
+--------+----------+


# group by + having
## having  Conditional expression ： Used to specify some conditions to output query results after grouping query .having  Function and  where  equally , but  having  It can only be used for  group by
mysql> select name,sum(score) as score_count from  test_table group by name having score_count >= 200;
+--------+-------------+
| name   | score_count |
+--------+-------------+
|  Xiao Ming    |       220.4 |
|  Xiaohong    |       210.3 |
|  Small blue    |       247.8 |
+--------+-------------+


# group by + with rollup
## with rollup  The role of is ： Add a new line at the end , To record the sum of all records in the current column 
mysql> select name,sum(score) as score_count from  test_table group by name with rollup;
+--------+-------------+
| name   | score_count |
+--------+-------------+
|  Little misery    |        92.6 |
|  Xiao Ming    |       220.4 |
|  Xiaohong    |       210.3 |
|  Small blue    |       247.8 |
| NULL   |       771.1 |
+--------+-------------+

Pagination 、 Link query 、 Subquery

#  Paging query 
## select * from  Table name  limit start,count  ## from  start  Start , obtain  count  Data 
###  Example :  Show the top 5 Data 
mysql> select * from test_table limit 5;
+----+--------+-----+-------------+-------+
| id | name   | age | create_date | score |
+----+--------+-----+-------------+-------+
|  1 |  Xiao Ming    |  18 | 2021-09-26  |  94.5 |
|  2 |  Xiaohong    |  17 | 2021-09-26  |  99.4 |
|  3 |  Small blue    |  18 | 2021-09-26  |  88.6 |
|  5 |  Xiaohong    |  17 | 2021-09-26  |  22.7 |
|  6 |  Xiaohong    |  17 | 2021-09-26  |  88.2 |
+----+--------+-----+-------------+-------+

#  Link query 
##  preparation  ( establish a、b  The two tables )
mysql> create table a(
    -> id int not null auto_increment,
    -> name varchar(15) not null,
    -> age int not null,
    -> primary key (id)
    -> );

mysql> create table b(
    -> id int not null auto_increment,
    -> uid int,
    -> gender varchar(15),
    -> primary key (id)
    -> );

##  Add data to the two tables 
mysql> insert into a(id,name,age) values
    -> (1,'A',18),
    -> (2,'B',19),
    -> (3,'C',20);

mysql> insert into b(id,uid,gender) values
    -> (1,1,'F'),
    -> (2,2,'M');

#  Start connection query 
##  Internal connection :  The result of the query is the data matched by the two tables 
mysql> select a.*,b.uid,b.gender from a inner join b  on a.id = b.id;
+----+------+-----+------+--------+
| id | name | age | uid  | gender |
+----+------+-----+------+--------+
|  1 | A    |  18 |    1 | F      |
|  2 | B    |  19 |    2 | M      |
+----+------+-----+------+--------+

##  External connection  -  The left outer join  (A left join B)
##  All data in the left table are reserved , The right table shows the records that meet the connection conditions , The records of unsatisfied conditions are all null
mysql> select a.*,b.gender from a left join b on a.id=b.uid;
+----+------+-----+--------+
| id | name | age | gender |
+----+------+-----+--------+
|  1 | A    |  18 | F      |
|  2 | B    |  19 | M      |
|  3 | C    |  20 | NULL   |
+----+------+-----+--------+

##  External connection  -  Right connection  (A right join B)
##  All data in the right table is reserved , The left table shows the records that meet the connection conditions , The records of unsatisfied conditions are all null
mysql> select b.*,a.name,a.age from a right join b on a.id=b.uid;
+----+------+--------+------+------+
| id | uid  | gender | name | age  |
+----+------+--------+------+------+
|  1 |    1 | F      | A    |   18 |
|  2 |    2 | M      | B    |   19 |
+----+------+--------+------+------+

#  Subquery #
##  In a  select  In the sentence , Embedded in another  select  sentence , So embedded  select  Statements are called subquery statements 
##  The relationship between main query and sub query :  Subqueries are embedded in the main query ; The subquery is auxiliary to the main query , Or as a condition , Or act as a data source ; Subqueries are statements that can exist independently , It's a complete  select  sentence 
###  A single simple example ：
mysql> select * from a where id = (select id from b where id=1);
+----+------+-----+
| id | name | age |
+----+------+-----+
|  1 | A    |  18 |
+----+------+-----+

Backup 、 recovery

#  The backup data 
##  Back up all data 
mysqldump -u root -p -A > all.sql

##  Back up a single library 
mysqldump -u root -p test_mysql > test_mysql.sql

## gzip  Compressed backup 
mysqldump  -u root -p test_mysql | gzip > test_mysql.sql.gz


#  Restore data 
##  Recover all data 
mysql -u root -p < all.sql   

##  Import a single library ( The imported library must exist )
1. create database test_mysql charset=utf8;
2. mysql -u root -p test_mysql < test_mysql.sql

## gunzip  Restore data 
gunzip < test_mysql.gz | mysql -u root -p test_mysql

management 、 to grant authorization

#  View all users 
##  Switch database 
mysql> use mysql;

'''
host:  Hosts allowed to access   
user:  Represents the user name   
authentication_string:  The password , Encrypted value 
'''
mysql> select user,host,authentication_string from use; 

#  Account management 

##  Create user 
mysql> create user 'test_root'@'%' identified by '111111';

##  rename user 
mysql> rename user 'test_root'@'%' to 'test_admin'@'%';

##  Change Password 
### 1. set password
mysql> set password for 'test_admin'@'%' = password('123456');

### 2. mysqladmin  Format ：mysqladmin -u user name  -p Old password  password  New password  
mysqladmin -u test_admin -p123456 password 111111

##  Delete user 
mysql> drop user 'test_root'@'%';


#  to grant authorization 
'''
 You need to use the instance level account to log in and operate , With  root  For example 
 Common permissions mainly include ：create、alter、drop、insert、update、delete、select
 If all permissions are assigned , have access to  all privileges
'''
##  Authorize users , If the user does not exist , Automatically created 
mysql> grant create,select,update,insert on test_mysql.* to 'test_root'@'%' identified by '111111';

##  Modify the permissions  ( Add a new permission to the original permission )
mysql> grant drop,delete,select on test_mysql.* to 'test_root'@'%' with grant option;

##  Delete permission   revoke  jurisdiction  on  database . surface  from ' user '@' Address ';
mysql> revoke delete on test_mysql.* from 'test_root'@'%';

##  View permissions 
mysql> show grants for 'test_root'@'%';

##  Refresh Authorization 
mysql> flush privileges;