MySQL statement

 database 
show databases;																			// View all databases 
select database(); 																		// View the current database 
create database [if not exists]  Database name  [default charset  Character set ] [collate  Sort rule ]; // Create database  
show create database  Database name ;														// view the database 
drop database [if exists]  Database name ;													// Delete database 
use  Database name ;																			// Using a database 
alter database  Database name 	character set  Character set ;										// Database character set modification 

 surface 
show tables;																			// Query all tables in the current database 
show create table  Table name ;																	// View table's MySQL command  
create table  Table name ( Field 1  Field type , Field 2  Field type ...  Field n  Field type );						// Create table 
desc  Table name ;																				// View table structure 
alter table  Table name  add  Field name   type ;                                                       // Add table fields 
alter table  Table name  modify  Field name   New data types ;												// Modify the table field type 
alter table  Table name  change  Old field name   new field name   type ;                                         // Modify the field name and field type 
alter table  Table name  drop  Field name ;															// Delete table fields 
alter table  Table name  rename to  The new name of the table ;														// Modify the name of the table 
drop table [if exists]  Table name ;															// Delete table 
truncate table  Table name ;																	// Delete and rebuild table 
	
 Data control language 
use mysql;  select * from user;															// Query the user 
create user ' user name '@' Host name ' identified by ' password ';										// Create user 
alter user ' user name '@' Host name ' identified with mysql_native_password by ' New password ';			// Change Password 
drop user ' user name '@' Host name '																// Delete user 
show grants for ' user name '@' Host name ';														// Query authority 
grant  Permission list  on  Database name  to ' user name '@' Host name ';										// Grant authority 
revoke  Permission list  on  Database name . Table name  from ' user name '@' Host name ';								// Revoke authority 

CRUD
select  Field 1, Field 2, Field 3 ... from  Table name 													// Query field 
select  Field 1 [as  Alias 1],  Field 2 [as  Alias 2] ... from  Table name ;								// set a table name 
select distinct  Field list  from  Table name ;														// duplicate removal 
select  Field list  from  Table name  where  Field  in( value 1, value 2...);									//in Inquire about 
select  Field list  from  Table name  where  Field  between  value 1 and  value 2;								//between...and...
select  Field list  from  Table name  where  Field  is not null;										// Null value query 
select  Field list  from  Table name  where  Conditions  and  Conditions ;											//and Inquire about 
select  Field list  from  Table name  where  Conditions  or   Conditions ; 											//or Inquire about 
select  Field list  from  Table name  where  Field  like ' Matching condition ';									//like Inquire about 
select  Field list  from  surface 1, surface 2 where  Conditions ...;												// Implicit inner join 
select  Field list  from  surface 1 [inner] join  surface 2 on  Connection condition ...;								// Explicit inner connection 
select  Field list  from  surface 1 left [outer] join  surface 2 on  Conditions ...; 								// The left outer join 
select  Field list  from  surface 1 right [outer] join  surface 2 on  Conditions ...; 							// Right connection 
select  Field list  from  surface A  Alias A join  surface A  Alias A on  Conditions ...;								// Self join 
select  Field list  from  surface A... union [all] select  Field list  from  surface B;						// The joint query 
select * from class where cid=(select classid from student where sname=' Zhang San ');			// A subquery with a comparison operator 
select * from class where exists (select * from student where sname=' Wang Wu ');			// belt EXISTS Subqueries for keywords  EXISTS The parameter after the keyword can be any subquery ,  It does not generate any data, only returns TRUE or FALSE. When the return value is TRUE The outer layer query will   perform 
select * from class where cid > any (select classid from student);						// belt ANY Subqueries for keywords  ANY Keyword means that if any of these conditions is met, a result will be returned as the outer query condition .
select * from class where cid > all (select classid from student);						// belt ALL Subqueries for keywords   belt ALL The result returned from the sub query of keyword must meet all internal query conditions at the same time .
	
INSERT INTO  Table name （ Field name 1, Field name 2,...) VALUES ( value  1, value  2,...);							// insert data 
INSERT INTO  Table name  [( Field name 1, Field name 2,...)]VALUES ( value  1, value  2,…),( value  1, value  2,…),...;			// Batch insert 

UPDATE  Table name  SET  Field name 1= value 1[, Field name 2 = value 2,…] [WHERE  Conditional expression ];						// Modifying data 

DELETE FROM  Table name  [WHERE  Conditional expression ];													// Delete data 

 constraint 
 Field name   data type  primary key;															// Primary key constraint 
 Field name   data type  NOT NULL;															    // Non empty constraint 
 Field name   data type  DEFAULT  The default value is ;														// Default constraint 
 Field name   data type  UNIQUE;																	// Unique constraint 
 Field name   data type  check;																	// Check constraint 


--  When creating a data table, the syntax is as follows ： // Foreign key constraints 
CONSTRAINT  Foreign key name  FOREIGN KEY ( From the table foreign key field ) REFERENCES  Main table  ( Primary key field )
--  The syntax after creating the number of the data table is as follows ：
ALTER TABLE  From the table name  ADD CONSTRAINT  Foreign key name  FOREIGN KEY ( From the table foreign key field ) REFERENCES  Main table  ( Primary key field );
alter table  From the table name  drop foreign key  Foreign key name ;											// Delete foreign key 
alter table  From the table name  drop foreign key  Foreign key name  foreign key ( Foreign key field ) references 			// Delete / Update behavior 
	 Main table name  ( Main table field name ) on update [no action/restrict/cassade/set null/set default] on delete [no action/restrict/cassade/set null/set default];

 function 
 1. String function 
	concat,lower,upper,lpad,rpad,trim,substring
 2. Numerical function 
	ceil,floor,mod,rand,round
 3. Date function 
	curdate,curtime,now,year,month,day,date_add,datediff
 4. Flow function 
	if,ifnull,case[...]when...then...else...end;
	
 The transaction operations 
select @@autocommit;																	// View transaction submission method 
set @@autocommit;																		// Set the transaction submission method 
commit;																					// Commit transaction 
rollback;																				// Roll back the transaction 
select @@transaction_isolation	/  select @@tx_isolation; （ The old version ）					// View transaction isolation level 
set[session|global] transaction level {
   read uncommitted|repeatable read|serializable};  // Set the transaction isolation level 

 Storage engine 
create table  Table name ( Field 1  Field type , Field 2  Field type ...  Field n  Field type )engine=innodb;        // Create a search engine 
show engines;																			// View the storage engines supported by the current database 
alter table  Table name  type=InnoDB （ The old version ）   /  alter table  Table name  ENGINE=InnoDB;			// Modify the search engine 

 Indexes 
create [unique|fulltext] index index_name on table_name (index_col_name...);			// Create index 
show index from table_name;																// Look at the index 
drop index index_name on table_name;													// Delete index 
create index idx_xxxx on table_name(column(n));											// Create prefix index column(n)
select count(distinct email)/count(*) from tb_user;    select count(distinct substring(email,1,5))/count(*) from tb_user;  // Optimal prefix length 

sql Optimize 
show global status like 'com____';														// see sql Frequency of execution 
show variables like 'slow_query_log';													// View the slow query switch 
slow_query_log=1;																		// Turn on slow query 
long_query_time=2;																		// Slow query time setting 2s After that, slow query 

select @@have_profiling;																// Check whether the database supports profile details 
select @@profiling;																		// see profile Open state of the 
show profiles;																			// see profile Of sql Statement details 
set profiling=1;																		// Set up profile The state of 

explain/desc select  Field list  from  Table name  where  Conditions ;										// Get the information of the executed statement 

sql Tips 
explain select * from tb_user use index(index_user_pro) where profession=' Software Engineering ';	//use index;  Index is recommended 
explain select * from tb_user ignore index(index_user_pro) where profession=' Software Engineering ';	//ignore index;  Ignore using indexes 
explain select * from tb_user force index(index_user_pro) where profession=' Software Engineering ';	//force index;  Force index 

 Batch insert optimization 
mysql --local-infile -u root -p
set global local_infile=1;																// Turn on the switch to import data from the local load file 
select @@local_infile;																	// View the local import data switch status 
load data local infile 'D:\\test.txt' into table employee fields terminated by';' lines terminated by '\n';	//load Instructions , Load local file data into the table structure 

 View 
create [or replace] view  View name [( view column list )] as select sentence  [with[cascaded | local] check option];	// Create view 
show create view  View name ;																			// View the create view statement 
select * from  View name ...;																			// View view data 
 Modify the view 1: create [or replace] view  View name [( view column list )] as select sentence  [with[cascaded | local] check option];  cascaded Will be passed to the upper level of the reference ,local Only apply to the statement 
 Modify the view 2: alter view  View name [( List of names )] as select sentence  [with [cascaded | local] check option];
drop view [if exists]  View name  [, View name ]...;														// Delete view 

 stored procedure 
create procedure  stored procedure ([ parameter list ])																// Create , If at the command line delimiter $$ Set up sql Statement terminator is $$
begin
	--SQL sentence 
end;

call  name ([ Parameters ]);																					// call 
select * from information_schemaroutines where routine_schema='xxx';								// Query the stored procedure and status information of the specified database 
show create procedure  Stored procedure name ;																	// Query the definition of a stored procedure 
drop procedure [if exists]  Stored procedure name ;															// Delete 

show [session | global] valables;																	// See all system variables 
show [session | global] variables like '...';														// Fuzzy query of all system variables 
select @@[session | global]  System variable name ;																// View the value of the specified variable 
set [session | global]  System variable name = value ;																// Set system variables 
set @@[session | global]  System variable name = value ;																

set @var_name=expr [,@var_name=expr]...;															// assignment 
set @var_name:=expr[,var_name:=expr]...;
select @var_name:=expr[,@var_name:=expr]...;
select  Field name  into @var_name from  Table name ;

select @var_name;																					// Use 
 local variable 
create procedure p2()
begin
	declare stu_count int default 0;// Create local variables 
	select count(*) into stu_count from student;// Assignment variable 
	select stu_count;// View the result of assignment 
end;
call p2();// Use 
if Judge 
create procedure p3()
begin
	declare score int default 58;
	declare result varchar(10);
	if score>=85 then
		set result := ' good ';
	elseif score >=60 then
		set result := ' pass ';
	else
		set result := ' fail, ';
	end if;
	select result;
end;
call p3();

 Parameters 
create procedure  Stored procedure name  ([in/out/inout  Parameter name   Parameter type ])
begin
	--SQL sentence 
end;

 example ：
create procedure p4(in score int,out result varchar(10))
begin	
	if score>=85 then
		set result := ' good ';
	elseif score >=60 then
		set result := ' pass ';
	else
		set result := ' fail, ';
	end if;
end;
call p4(68,@result);
select @result;

case grammar 
 Grammar 1 ：
case case_value
	when when_value1 then statement_list1
	[when when_value2 then statement_list2]...
	[else statement_list]
end case;
 Grammar II ：
case
	when search_condition1 then statement_list1
	[when search_condition2 then statement_list2]...
	[else statement_list]
end case;

while grammar 
while  Conditions  do
	sql Logic 
end while;
 for example ：
create procedure p7(in n int)
begin
	declare total int default 0;
	while n>0 do
		set total:=total+n;
		set n:=n-1;
	end while;
	select total;
end;

repeat grammar  // Exit when conditions are met 
repeat
	sql Logic 
	until  Conditions 
end repeat
 for example ：
create procedure p8(in n int)
begin
	declare total int default 0;
	repeat
		set total := total+n;
		set n:=n-1;
	until n<0;
	end repeat;
	
	select total;
end;

loop grammar 
[begin_label:] loop grammar 
	sql Logic 
end loop [end_label];

leave label; -- Exit the currently marked loop body 
iterate label; -- Go directly to the next cycle 
 for example ：
create procedure p10(in n int)
begin
	declare total int default 0;
	sum:loop
		if n<=0 then	
			leave sum;
		end if;
		
		if n%2=1 then
			set n := n-1;
			iterate sum;
		end if;
		
		set total := total + n;
		set n:n-1;
	end loop sum;
end;

 The cursor 
declare  Cursor name  cursor for  Query statement ;						// declare cursor 
open  Cursor name ;												// Open cursor 
fetch  Cursor name  into  Variable  [, Variable ];							// Get cursor record 
close  Cursor name ;												// Close cursor 
 Condition handler 
declare hander_action handlerfor condition_value [,condition_value]... statement;

hander_action
		continue: Continue with the current program 
		exit: Terminate the execution of the current program 
condition_value
		sqlstate sqlstate_calue: Status code , Such as 02000
		sqlwarning: All with 01 At the beginning sqlstate Code abbreviation 
		not found: All with 02 At the beginning sqlstate Code abbreviation 
		sqlexception: All have not been sqlwharning and not found The captured sqlstate Code abbreviation 

 for example ：
create procedure p11(in uage int)
begin
	declare uname varchar(100);
	declare upro varchar(100);
	declare u_cursor cursor for select name,profession from tb_user where age<=uage;
	declare exit handler for sqlstate '02000' close u_cursor;
	
	drop table if exists tb_user_pro;
	create table if not exists tb_user_pro{
		id int primary key auto_increment;
		name varchar(100);
		profession varchar(100)
	};
	
	open u_cursor;
	while true do
		fetch u_cursor into uname,upro;
		insert into tb_user_pro values(null,uname,upro);
	end while;
	close u_cursor;

 trigger 
create trigger trigger_name                          			// establish 
before/after insert/update/delete on tbl_name for rach row -- Line level triggers 
begin
	triger_stmt;      // Trigger specific logic statement 
end;
 for example ：
create trigger tb_user_insert_trigger
	after insert on tb_user for each row
begin	
	insert into user_logs(id,name) values (null,'insert',new id,new.name);
end;


show trigger;													// see 
drop trigger [schema_name.]trigger_name;                        // Delete   If there is no designated schema_name, The default is the current database 

 lock 
	 Global lock 
	flush tables with readlock;                                 // Set global lock 
	mysqldump -single-transaction -uroot -p123456 itcast>itcast.sql; // Data consistent backup without lock ( snapshot ) 
	unlock tables;												// Unlock the global lock 
	 Table lock 
	lock tables  Table name ... read/write                              // Lock 
	unlock tables/ Client disconnected 								// Release the lock 
	select...lock in share mode                                  // Intention sharing lock 
	insert/update/delete/select...for update                          // Intention exclusive lock