MySQL - SQL statement

Log in to the database

##  Ciphertext password to enter 
mysql -uroot -p

##  Plaintext password entry 
mysql -uroot -p  password 

-u user name 
-hIP
-p password 

notes

Single-line comments “ - - ”

• -- And there is a space in the comment content

--  The comment 

Single-line comments “#”

# The comment 

Multiline comment “/**/”

/* The comment */

Inline comments “/*! */”

/*! The comment */

sign out 、 help

operation
Exit database	exit、\q、quit
help	help
Query command	help Some commands

DDL	Data definition language	create、drop
DML	Data operation language	crud、insert、update、select
DCL	Data control language	grant、revoke

Select database use

mysql> use  Database name ;
Database changed
mysql>

establish create

Create database

Be careful

• The database name is in English
• Do not use the same name as the original database

grammar

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
// Create common database ;[IF NOT EXISTS] Indicates when does not exist 

    [DEFAULT] CHARACTER SET [=] charset_name
    // Set the encoding format 
  	[DEFAULT] COLLATE [=] collation_name

Example

// Create database 
CREATE DATABASE  Database name ;

// be known as   Database name   The database for does not exist , Then create 
CREATE DATABASE IF NOT EXISTS  Database name ;

// be known as   Database name   The database for does not exist , Then create ; And the code is utf8mb4
CREATE DATABASE IF NOT EXISTS  Database name  CHARACTER SET utf8mb4;

Create data table

establish MySQL Data tables need the following information ：

• Table name
• Table field name Column names need not be quoted
• Define each table field

CREATE TABLE  Table name  (     Name   data type  [ constraint condition ],     Name   data type  [ constraint condition ],     Name   data type  [ constraint condition ]);

CREATE TABLE IF NOT EXISTS  Table name (     Name  INT(10),     Name  INT(10) AUTO_INCREMENT Unique,     Name  INT(10) AUTO_INCREMENT PRIMARY KEY,     Name  INT UNSIGNED AUTO_INCREMENT PRIMARY KEY NOT NULL,     Name  INT (10) UNSIGNED AUTO_INCREMENT PRIMARY KEY NOT NULL,     Name  VARCHAR(2),     Name  VARCHAR(2) NOT NULL,     Name  VARCHAR(2) NOT NULL default “m” check ( Name  in ("m","f")),     Name  DATE,    PRIMARY KEY ( Name , Name , Name ))ENGINE=InnoDB DEFAULT CHARSET=utf8;)ENGINE=InnoDB DEFAULT CHARACTER SET utf8mb4;

• IF NOT EXISTS ： If it doesn't exist

• IF EXISTS ： If there is

• AUTO_INCREMENT ： Define properties that are listed as self incrementing , Generally used for primary key , The value will be added automatically 1;

  • Each table can only have 1 Automatic growth fields , The auto increment field is Primary key Or there is unique index
  • If the auto growth field is set to non primary key, an error will be reported if no unique index is added --> id int auto_increment

• NOT NULL ： When operating the database, if the data entered in this field is NULL , You're going to report a mistake

• PRIMARY KEY ： Used to define columns as primary keys ; You can use multiple columns to define the primary key , Columns are separated by commas

  • Use PRIMARY KEY After the field defines the primary key , You cannot use it to create multiple primary keys at the end ; Can only be used once

• default “m” check (sgender in (“m”,“f”)) ： Can only write m or f

• ENGINE Set up the storage engine

• CHARSET Set encoding

Create database mysqladmin

[[email protected]]# mysqladmin -u root -p create  Database name Enter password:******

Copy the structure of the table

Copy structure

create table  The new name of the table  like  Source table 

Copy structure 、 data

create table  The new name of the table  select * from  Source table 

Delete drop

Delete database

Format ：

drop database  Database name ;

Delete data table

grammar

DROP TABLE  Table name  ;

mysqladmin

[[email protected]]# mysqladmin -u root -p drop  Database name Enter password:******

database [y/N] y

insert data insert

• insert data character 、 date (2000-1-1) Need quotes

INSERT INTO table_name ( field1, field2,...fieldN )VALUES ( value1, value2,...valueN );

• example

INSERT INTO table_name ( field1, field2,...fieldN )VALUES ( 'value1','value2','...valueN' );INSERT INTO table_name ( field1, field2,...fieldN )VALUES ( "value1", "value2","...valueN" );

Copy table information

Same structure

insert into  Table name  select * from  Data sheet  [where];

The structure is different

insert into  Table name ( Name ) select  Name  from  Data sheet  [where];

to update UPDATE

UPDATE table_name SET field1=new-value1, field2=new-value2[WHERE  Column ="a"]

Delete DELETE

DELETE FROM table_name [WHERE Clause]

Clear the table truncate

truncate  Table name 

View table format

describe  Table name ;desc  Table name ;

see show

View all libraries in the database

show databases

View the tables in the library

show tables

View basic database information

show create database  Database name ;+----------+----------------------------------------------------------------+| Database | Create Database                                                |+----------+----------------------------------------------------------------+| mm       | CREATE DATABASE `mm` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |+----------+----------------------------------------------------------------++----------+-------------------------------------------------------------------------------------+| Database | Create Database                                                                     |+----------+-------------------------------------------------------------------------------------+| mh       | CREATE DATABASE `mh` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci */ |+----------+-------------------------------------------------------------------------------------+

View the creation information of the table

show create table  Table name ;+-------+--------------------------------------------------------------------------------------------------+| Table | Create Table                                                                                     |+-------+--------------------------------------------------------------------------------------------------+| zw    | CREATE TABLE `zw` ( `id` int(11) NOT NULL AUTO_INCREMENT,`name` varchar(20) DEFAULT NULL,`sex` varchar(5) DEFAULT ' male ',PRIMARY KEY (`id`)) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci|+-------+--------------------------------------------------------------------------------------------------+

Modify table ALTER

ALTER {DATABASE | SCHEMA} [db_name]ALTER {DATABASE | SCHEMA} db_name    UPGRADE DATA DIRECTORY NAME    [DEFAULT] CHARACTER SET [=] charset_name    // Modify character set     [DEFAULT] COLLATE [=] collation_name

Modify the character set of the database

• View character set

show variables 1ike'characeer%';

• Modify database character set

alter database testdb character set utf8;alter database testdb default character set utf8;// Modify the character set of the database , And set as the default character set , All tables in the database will inherit this character set 

Modify the name of the table

• Use ALTER TABLE Use in statement RENAME Clause to implement

# Try the following example to put the data table  testalter_tbl  Rename it to  alter_tbl：ALTER TABLE testalter_tbl RENAME TO alter_tbl;

Add columns

ALTER TABLE  Table name  ADD  Name  INT [ constraint condition ];## The default value is 0ALTER TABLE  Table name  ADD  Name  INT default 0;

• Location
  • Columns are added to the end of the data table fields by default
  • FIRST ( Set the first column )
  • AFTER Field name （ Set after a field ）

ALTER TABLE  Table name  ADD  Name  INT FIRST;ALTER TABLE  Table name  ADD  Name  INT AFTER  Name ;

Try the following ALTER TABLE sentence , After successful execution , Use SHOW COLUMNS See changes in table structure

Delete table fields

• If there is only one field left in the data table, it cannot be used DROP To delete fields

• The following command is used ALTER Orders and DROP Clause to delete the i Field

ALTER TABLE  Table name   DROP  Name ;

Modify column type

• Modification type MODIFY

ALTER TABLE  Table name  MODIFY  Name   new type  [ constraint condition ];

Change the name type CHANGE

• stay CHANGE After keyword , Next comes the field name you want to modify , Then specify the new field name and type

ALTER TABLE testalter_tbl CHANGE  Old column names   New column names   new type  [ constraint condition ];

Modify field defaults

• Use ALTER To change the default value of the field

ALTER TABLE testalter_tbl ALTER i SET DEFAULT 1000;

• Use ALTER Orders and DROP Clause to delete the default value of the field

ALTER TABLE testalter_tbl ALTER i DROP DEFAULT;

• Modify data table type , have access to ALTER Orders and TYPE Clause

• ** Be careful ：** You can use... To view data table types SHOW TABLE STATUS sentence .

ALTER TABLE testalter_tbl ENGINE = MYISAM;SHOW TABLE STATUS LIKE 

Delete table constraints

• Delete not null constraint

alter table  Table name  modify  Name   type  [ constraint ];

• Delete unique constraint

alter table  Table name  drop index  Unique constraint name ;

• Delete primary key constraint

alter table  Table name  drop primary key;

• Delete foreign key constraint

alter table  Table name  drop foreign key  Foreign key name ;

ALTER TABLE Yes Null The effect of values and defaults

• When you modify fields , You can specify whether to include values or whether to set default values
• If you don't set the default value ,MySQL It will automatically set the default value of this field to NULL

# Specified field  j  by  NOT NULL  And the default value is 100ALTER TABLE testalter_tbl MODIFY j BIGINT NOT NULL DEFAULT 100;

Inquire about select

grammar

SELECT  Name , Name FROM  database . Table name , database . Table name [WHERE  Conditions ][LIMIT N][ OFFSET M]

• * wildcard Represents all columns

• You can query multiple tables using , separate

• SELECT Command can read One or more records .

• You can use LIMIT Property to set the number of records returned .

• You can go through OFFSET Appoint SELECT Statement start query data offset . By default, the offset is 0.

Query current user

select user();

Querying the current database

select database()

View version

select version();

Choice judgment WHERE

grammar

SELECT  surface . Name [, surface . Name ,...] 	FROM  surface [, surface ,...]    [WHERE  Conditions ]      [GROUP BY  Name ]    [HAVING  Conditions ]    [ORDER BY .....]    [LIMIT .......]

SELECT  Name ,  Name ,... FROM  Table name 1,  Table name 2...WHERE  Conditions 

Conditions

WHERE  Name <100WHERE  Name  is nullWHERE  Name <=>nullWHERE  Name  is not nullWHERE  Name  IN (1,2,3)WHERE  Name  LIKE "3%"WHERE  Name  IN (1,2,3)

• You can use AND perhaps OR Specify one or more conditions

WHERE  Conditions 1 AND  Conditions 2.....WHERE  Conditions 1 OR   Conditions 2.....

The examples in the following table assume A by 10, B by 20

The operator	describe	example
=	Equal sign , Check if two values are equal , If equal returns true	(A = B) return false
<=>	Safety equal sign , It is equal to	(A = B) return false
<>, !=	It's not equal to , Check if two values are equal , If not equal return true	(A != B) return true
>	More than no. , Check whether the value on the left is greater than the value on the right , If the value on the left is greater than the value on the right, return true	(A > B) return false
<	Less than no. , Check if the value on the left is less than the value on the right , If the value on the left is less than the value on the right, return true	(A < B) return true
>=	Greater than or equal to , Check whether the value on the left is greater than or equal to the value on the right , If the value on the left is greater than or equal to the value on the right, return true	(A >= B) return false
<=	Less than or equal to sign , Check whether the value on the left is less than or equal to the value on the right , If the value on the left is less than or equal to the value on the right, return true	(A <= B) return true

• If the given condition does not have any matching records in the table , So the query doesn't return any data

List query IN

 Name  IN ( list ) Name  NOT IN ( list )

• Try not to use ,in Will abandon the index , Perform a full table scan

Fuzzy query LIKE

 Name  LIKE ‘3%’

• Give up the index , A full table query , Low efficiency

Symbol	explain
‘a%’	With a start
‘%a%’	contain a
‘_a%’	The second letter is a

• **% ** Represents any number of arbitrary characters
• _ Represents a character

Regular expressions regexp

 Name  regexp '^root'

Range queries BETWEEN

 Name  between 1000 AND 1500

• Closed interval

Sort ORDER BY

SELECT  Name ,  Name ,... FROM  Table name 1,  Table name 2...ORDER BY  Name  [ASC [DESC][ Default  ASC]], [field2...] [ASC [DESC][ Default  ASC]]

• ASC Ascending 、 DESC Descending

grouping GROUP BY

SELECT column_name, function(column_name)FROM table_nameWHERE column_name operator valueGROUP BY column_name;

• Put the same results in a group
• We can use... On grouped columns COUNT, SUM, AVG, Such as function .

SELECT sex,count(sex) from gxsf group by sex;

Screening HAVING

SELECT column_name, aggregate_function(column_name)FROM table_nameWHERE column_name operator valueGROUP BY column_nameHAVING aggregate_function(column_name) operator value;

Pagination LIMIT

SELECT * FROM COMPANY LIMIT  Number of pieces ;SELECT * FROM COMPANY LIMIT  The starting position , Number of pieces ;

SELECT * FROM COMPANY LIMIT 4;SELECT * FROM COMPANY LIMIT 4,4;

where and having Then there are screening criteria , But there is a difference ：

• where stay group by front , having stay group by after

• Aggregate functions （avg、sum、max、min、count）, Cannot be placed as a condition on where after , But you can put it in having after

operation

operation	result	explain
SELECT 100+80	180	Perform normal operations
SELECT 100+‘80’	180	Convert characters to numbers , Carry out operations
SELECT 100+‘abc’	100	Convert characters to numbers , Cannot be converted 0
SELECT ‘THIS’+‘IS’	0	Convert characters to numbers , Cannot be converted 0
SELECT NULL+80	NULL	One of the values is NULL, The result is NULL

Multi-table query

• No relation is specified in the query , The database could not determine the association relationship , Just match them all , There will be Cartesian product

select  Table name . Name , Table name . Name  from  Table name , Table name  where  Table name . Name = Table name . Name ;

Connect

Internal connection

• INNER JOIN（ Internal connection , Or equivalent connection ）： Get the records of field matching relationship in two tables

select  Table name . Name , Table name . Name  from  Table name  [inner] join  Table name  on( Table name . Name = Table name . Name );

SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a INNER JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; above  SQL  Statement is equivalent to ：SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a, tcount_tbl b WHERE a.runoob_author = b.runoob_author;

External connection

• **LEFT JOIN（ Left connection ）：** Mainly in the left table , Show all , Even if there is no matching record on the right
• **RIGHT JOIN（ The right connection ）：** Get all the records in the right table , Even if the left table does not have a matching record

select  Table name . Name , Table name . Name  from  Table name  left join  Table name  on( Table name . Name = Table name . Name );

select  Table name . Name , Table name . Name  from  Table name  right join  Table name  on( Table name . Name = Table name . Name );

Self join

• The table itself is associated with itself ：
• The result of each query is also a table

	surface
id	name	up_id
1	The Internet	null
2	linux	null
3	Router	1
4	Switch	1

select inter.name,a.name upfrom inter left join (select id,name from inter where up_id is null) a on (inter.up_id=a.id)where up_id is not null;

Subquery

select * from  Table name  where  Name =(select  Name  from  Table name  [where])

select * from  Table name ,select  Name  from  Table name  [where]

The joint query UNION

describe

MySQL UNION Operators are used to connect more than two SELECT The results of a statement are combined into a set of results . Multiple SELECT Statement will remove duplicate data .

• The number of columns in two query statements should be the same

grammar

SELECT expression1, expression2, ... expression_nFROM tables[WHERE conditions]UNION [ALL | DISTINCT]SELECT expression1, expression2, ... expression_nFROM tables[WHERE conditions];

Parameters

• DISTINCT: Optional , Delete duplicate data in result set . By default UNION The operator has removed the duplicate data , therefore DISTINCT Modifiers have little effect on the results .
• ALL: Optional , Return all result sets , Contains duplicate data .

View the summary information of the current database and current connection

status

status--------------mysql  Ver 14.14 Distrib 5.7.26, for Win64 (x86_64)Connection id:          7Current database:       mmCurrent user:           [email protected]:                    Not in useUsing delimiter:        ;Server version:         5.7.26 MySQL Community Server (GPL)Protocol version:       10Connection:             localhost via TCP/IPServer characterset:    utf8Db     characterset:    utf8mb4Client characterset:    utf8Conn.  characterset:    utf8TCP port:               3306Uptime:                 3 hours 10 min 28 secThreads: 1  Questions: 42  Slow queries: 0  Opens: 340  Flush tables: 1  Open tables: 37  Queries per second avg: 0.003--------------

 Currently linked id No. whether the currently linked login user of the currently selected database used ss! The line terminator of the current session is a semicolon mysql Version is mariadb Branch current mysql The version number of the server the link type used by the protocol version , Connect through the socket file of this computer. The character type used by the server is the current character type used by the database mysql The character type used by the client the character type used by the current link the start time of the socket file path database 

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