[Database Foundation] summary of MySQL Foundation

1、MySql Start up and connect

Server startup ：

• see mysql state ：sudo /etc/init.d/mysql status
• Start the service ：sudu /etc/init.d/mysql start | stop | restart

Client connection ：

• Command format ：

  • mysql -h The host address -u user name -p password , Such as ：

    mysql -hlocalhost -uroot -p123456, Local connections can be omitted -h Options ：mysql -uroot -p123456

• Close the connection ：

  • quit
  • exit

2、 Database operation

2.1、 View existing libraries

show databases;		-- Keywords are not case sensitive , Parameter differentiation 

2.2、 Create a library （ Specify character set ）

create database Library name [character set utf8];

create database test_book character set utf8;		-- or 
create database test_book character=utf8;

2.3、 View character set

show create database stu;

2.4、 View the current library

select database();

2.5、 Switch Library

use stu;

2.6、 Delete Library

drop database test;

3、 Data table management

3.1、 Data type support

3.1.1、 Numeric type

Integer types ：

• TINYINT：1 byte

• SMALLINT：2 byte

• MEDIUMINT：3 byte

• INT：4 byte

• BIGINT：8 byte

  Floating point type ：

• FLOAT：4 byte

• DOUBLE：8 byte

  Point type ：DECIMAL(M,D)

• M Is the maximum number of digits in a number , Range 1-65, The default value is 10

• D Is the number of digits to the right of the decimal point , Range 0-30, No more than M

• Such as ：DECIMAL(6,2), Save at most 6 Digit number , After the decimal point 2 position , The scope is -9999.99~9999.99

  Bit value type ：BIT

• 0,1 Values express two situations , Ruzhen , false

3.1.2、 String type

CHAR and VARCHAR type

• CHAR： Fixed length (0-255 byte ), Efficient , Default 1 character ,CHAR(32) Even if the string length is less than 32 Will also open up 32 Byte space . If the length is not specified , The default is 1
• VARCHAR(0-65535 byte )： Indefinite length , Low efficiency ,VARCHAR(32) It means to develop according to the actual situation , most 32 byte . Length... Must be specified .

BLOB type

• TINYBLOB： Storage 2 Base string （0-255 byte ）, For example, you can save pictures ;
• BLOB：0-65535 byte
• MEDIUMBLOB：0-16777215 byte
• LONGBLOB：0-4294967295 byte
• TEXT Storing text data ,

TEXT type

• TINYTEXT： Text string （0-255 byte ）, and VARCHAR The difference is that there is no need to specify the length
• TEXT：0-65535 byte
• MEDIUMTEXT：0-16777215 byte
• LONGTEXT：0-4294967295 byte

3.1.3、ENUM The type and SET type

• ENUM Enumeration type , Used to store a given value
• SET Collection types , Used to store one or more given values

3.1.4、 Date time type

• DATA：YYYY-MM-DD, Such as ：2022-06-15
• TIME：HH:MM:SS, Such as ：17:35:22
• YEAR：YYYY, Such as ：2022
• DATATIME：YYYY-MM-DD HH:MM:SS,8 byte , The scope is 1000-01-01 00:00:00~9999-12-31 23:59:59, Such as ：2022-06-15 17:35:22
• TIMESTAMP：YYYY-MM-DD HH:MM:SS,4 byte , The scope is 1970-01-01 00:00:01 UTC~2038-01-19 03:14:07 UTC, Such as ：2022-06-15 17:35:22

Commonly used date time function ：

now()		 Returns the current time of the server ,datetime,YYYY-MM-DD HH:MM:SS
curdate()	 Return current date ,date,YYYY-MM-DD, If the data type is datetime, Then for YYYY-MM-DD 00:00:00
curtime()	 Return current time ,time,HH:MM:SS, If the data type is datetime, Then the date will be automatically supplemented with the current date 
date(date)	 Returns the date at the specified time ,date
time(date)	 Returns the time of the specified time ,time

Date time operation ：

Grammar format ：

• select * from Table name where Field name Operator ( Time -interval Time interval unit );

• Time interval unit ：1 day | 2 hour | 1 minute | 2 year |3 month

  select * from xxx_table where shijian > now() - interval 1 day;
  

3.2、 Basic operation of the watch

3.2.1、 Create table

create table Table name (

Field name data type ,

Field name data type ,

…

Field name data type

)

tips：

• If you want to set the number to unsigned, add UNSIGNED

• If you don't want the field to be NULL You can set the field attribute to NOT NULL

• DEFAULT Indicates setting the default value of a field

• AUTO_INCREMENT Define the column as a self incrementing attribute , Generally used for primary key , The value will automatically increase by one

• PRIMARY KEY Keywords are used to define columns as primary keys , The primary key value cannot be duplicate

  Examples are as follows ：

CREATE TABLE book(
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(32) NOT NULL,
    type SET(' literature ',' history ',' Geography ',' Physics ',' mathematics '),
    public ENUM(' People's Literature Press ',' Electronic industry press ',' Mechanical industry press ',' Peking University press '),
    price decimal(7,2),
    introduce text,
    upt datetime default now()
);

3.2.2、 See the table

show tables;

3.2.3、 View the character set of the existing table

show create table  Table name ;

3.2.4、 View table structure

desc  Table name ;

3.2.5、 Delete table

drop table  Table name ;

4、 Data basic operation

4.1、 Insert insert

insert into  Table name  values( value 1, value 2, value 3...);		-- When no field is specified , All fields should be set with values 
insert into  Table name  ( Field 1, Field 2,...) values( value 1, value 2,...);
e.g.
insert into book values (1,' Long song line ',' literature , history ',' Peking University press ',52.2,' Tang legend ',now());
-- set use ',' separate 

give the result as follows ：

+----+--------+-----------+----------------+-------+--------------+---------------------+
| id | name   | type      | public         | price | introduce    | upt                 |
+----+--------+-----------+----------------+-------+--------------+---------------------+
|  1 |  Long song line  |  literature , history  |  Peking University press  | 52.20 |  Tang legend  | 2022-06-15 16:06:26 |
+----+--------+-----------+----------------+-------+--------------+---------------------+

4.2、 Inquire about select

select * from  Table name  [where  Conditions ];
select  Field 1, Field 2  Table name  [where  Conditions ];

where Clause ： Data filtering through certain operation conditions

select * from book where id % 2 = 1;		
-- lookup id All data with odd numbers 

select * from book where find_in_set(' history ',type);
-- lookup type contain ' history ' All data for 

select * from book where public like '__ university %';
--like For fuzzy query ,'_' Matches any character ,'%' Match any number of characters 

4.3、 to update update

update  Table name  set  Field 1= value 1, Field 2= value 2,... where  Conditions ;

e.g:
update book set price=38.8 where id=1;

4.4、 Delete delete

delete from  Table name  where  Conditions ;

e.g:
delete from book where id=8;

5、 Table field operation

 grammar ：alter table  Table name   Executive action ;


 Change data type ：modify


 Table rename 
alter table  Table name  rename  The new name of the table 

e.g.
alter table class add tel char(11) not null;	// Add to the end 
alter table class add height int after age;		// Add to age after 
alter table class add test int first;			// Add to beginning 

alter table class drop test;

alter table class modify height char(3);

alter table class change height weight int;

alter table class rename classnew;

5.1、 Add fields ：add

alter table  Table name  add  Field name   data type ;				-- Add... At the end 
alter table  Table name  add  Field name   data type  first;			-- Add... At the beginning 
alter table  Table name  add  Field name   data type  after  Field name ;	  -- Add... After a field 

5.2、 Delete field ：drop

alter table  Table name  drop  Field name ;

5.3、 Modify field name ：change

alter table  Table name  change  Old field name   new field name   New data types ;

5.3、 Change data type ：modify

alter table  Table name  modify  Field name   New data types ;

5.4、 Table rename ：rename

alter table  Table name  rename  The new name of the table ;

6、 Advanced query

6.1、 Regular queries ：REGEXP

• Regular queries ：regexp, Only some regular metacharacters are supported

select *
from table_name
where field1 regexp condition1;

-- e.g:
select * from book where public regexp '.*? north .*?';

6.2、 Sort ：ORDER BY

select * from book order by id;		--  Default ascending order asc;
select * from book where id%2=1 order by id desc;		-- id The query results with cardinality are sorted in descending order 

6.3、 Pagination ：LIMIT

limit Clause is used to restrict by select The number of data returned by statements , perhaps update,delete The number of operations of the statement , The basic grammar is as follows ：

select * 
from table_name
where field
limit [num];

-- e.g:
delete from book where price>50 limit 1;	--  Delete the first record found 
update book set price=20 limit 1;			--  The first record price It is amended as follows 20
select * from book where id%2=0 order by id desc limit 1;		--  Find the largest even number id

6.4、 The joint query ：UNION

UNION Operators are used to connect 2 More than one select The results of a statement are combined into a set of results , Multiple select Statement will delete duplicate data .

UNION Operator syntax format ：

select expression1,expression2,...expressionN
from tables
[where conditions]
union [all | distinct]
select expression1,expression2,...expressionN
from tables
[where conditions];

--  explain ：
-- all Do not do heavy work , Without or set to distinct Can do the heavy .
--  Different tables can also be queried jointly 

Example ：

Data in the database ：

+----+-------------------+----------------+----------------+-------+
| id | name              | type           | public         | price |
+----+-------------------+----------------+----------------+-------+
|  1 |  Long song line             |  literature , history       |  Peking University press  | 20.00 |
|  2 |  Short poetry             |  literature , history       |  Peking University press  | 52.20 |
|  3 | MySql From entry to abandonment  |  mathematics            |  Mechanical industry press  | 52.20 |
|  4 |  Journey to the west             |  literature , history , Geography  |  People's Literature Press  | 30.50 |
+----+-------------------+----------------+----------------+-------+

Query statement ：

select id,name,type,public,price 
from book 
where id>2 
union all 
select id,name,type,public,price 
from book 
where public=' People's Literature Press ';

Query results ：

+----+-------------------+----------------+----------------+-------+
| id | name              | type           | public         | price |
+----+-------------------+----------------+----------------+-------+
|  3 | MySql From entry to abandonment  |  mathematics            |  Mechanical industry press  | 52.20 |
|  4 |  Journey to the west             |  literature , history , Geography  |  People's Literature Press  | 30.50 |
|  4 |  Journey to the west             |  literature , history , Geography  |  People's Literature Press  | 30.50 |
+----+-------------------+----------------+----------------+-------+

Query statement ：

select id,name,type,public,price 
from book 
where id>2 
union distinct 
select id,name,type,public,price 
from book 
where public=' People's Literature Press ';

Query results ：

+----+-------------------+----------------+----------------+-------+
| id | name              | type           | public         | price |
+----+-------------------+----------------+----------------+-------+
|  3 | MySql From entry to abandonment  |  mathematics            |  Mechanical industry press  | 52.20 |
|  4 |  Journey to the west             |  literature , history , Geography  |  People's Literature Press  | 30.50 |
+----+-------------------+----------------+----------------+-------+

6.5、 Group query ：GROUP BY

select fieldx  Aggregate functions  
from  Table name 
where conditionx
group by fieldx
having conditionx
order by fieldx
limit n;

explain ：

• Aggregate functions ：avg、max、min、sum、count
• having To further screen the grouped results

Example ： stay id>0 The results of , Check the average price of all books in the publishing house , With avg_p Show , Only show that the average price is greater than 35 Result , Reverse order

select public,avg(price) as avg_p 
from book 
where id>0 
group by public 
having avg_p>35 
order by avg_p desc;

The query results are as follows ：

+----------------+-----------+
| public         | avg_p     |
+----------------+-----------+
|  Mechanical industry press  | 52.200000 |
|  Peking University press  | 36.100000 |
+----------------+-----------+

6.6、 nested queries （ Subquery ）

Take the query result of the inner layer as the query condition of the outer layer

select ... from  Table name  where  Conditions (select ...);

Example ： Check the most expensive books in each publishing house ：

select * from book where (public,price) in (select public,max(price) from book group by public);

6.7、 Multi-table query

select table1.field1,table2.field2,... 
from table1,table2 where table1.fieldn=table2.fieldn;

6.8、 Link query

Connection query is divided into internal connection 、 Left connection and right connection , The inner connection needs to match the left and right tables at the same time ; The left connection displays the query results mainly in the left table , The right table does not match the display NULL; The right connection displays the query results mainly in the right table , The left table does not match the display NULL;

The format is as follows ：

select  Field name  from  surface 1 inner join  surface 2 on  Conditions  inner join  surface 3 on Conditions ;

7、 Copy table

When copying a table, the original table will not be copied key attribute , The grammar is as follows ：

create table  Table name  select  Query command ;

Example ： Copy book Tabular id,name,public,price Field to new table , Take the first three data ：

create table copy_book select id,name,public,price from book limit 3;
select * from copy_book;

give the result as follows ：

+----+-------------------+----------------+-------+
| id | name              | public         | price |
+----+-------------------+----------------+-------+
|  1 |  Long song line             |  Peking University press  | 20.00 |
|  2 |  Short poetry             |  Peking University press  | 52.20 |
|  3 | MySql From entry to abandonment  |  Mechanical industry press  | 52.20 |
+----+-------------------+----------------+-------+

desc see ：

desc book;
desc copy_book;

result ：

8、 Data backup and recovery

8.1、 Backup

mysqldump -u user name -p Library name > ~/***.sql

Library name surface 1 surface 2 surface 3 Back up multiple tables of the specified library

mysqldump -uroot -p test_book > C:\databk\testbook.sql     
--  Backup Library test_book To C:\databk\testbook.sql Next 

mysqldump -uroot -p test_book book sale > C:\databk\testbook.sql     
--  Backup Library test_book Medium book sale Two tables to C:\databk\testbook.sql Next 

8.2、 recovery

mysql -uroot -p Target library name < ***.sql

--  Before recovery, if the database does not exist, you need to build the database first 
create database test_book character=utf8;
mysql -uroot -p test_book < C:\databk\testbook.sql