MySQL advanced (index, view, stored procedure, function, password modification)

Indexes

  mysql The index of is like the table of contents page of a dictionary （ Indexes ） equally , We can press Pinyin 、 stroke 、 A catalogue sorted by radicals, etc （ Indexes ） Quickly find the words you need .
   Indexes are divided into single column indexes and composite indexes . Single index , That is, an index contains only a single column , A table can have multiple single-column indexes , But this is not a composite index . Composite index , That is, an index contains multiple columns .
When you create an index , You need to make sure that the index is applied to SQL Conditions of query statement ( As a general WHERE Condition of clause ). actually , Index is also a table , The table holds the primary key and index fields , And points to the record of the entity table .
   Although indexing can speed up data retrieval , But using index too much will lead to abuse . So index also has its disadvantages ： Although the index greatly improves the query speed , At the same time, it will reduce the speed of updating the table , Such as on the table INSERT、UPDATE and DELETE. Because when updating tables ,MySQL Not only to save data , And save the index file . Index files that take up disk space .

General index

• Look at the index

show index from  Table name ;

• Create index

Mode one ： Create index when creating table

 CREATE TABLE create_index(
 id INT PRIMARY KEY,
 NAME VARCHAR(10) UNIQUE,
 age INT,
 INDEX age_index(age)
 );

Mode two ： For existing tables , Add index

// If the specified field is a string , You need to specify the length , The recommended length is the same as the length when defining the field 
// If the field type is not a string , You can leave out the length section 
create index  The index name  on  Table name ( Field name ( length ))
 example ：
create index age_index on create_index(age);
create index name_index on create_index(name(10));

• Delete index

drop index  The index name  on  Table name ;

• Turn on Runtime Monitoring

set profiling=1;

• Check the execution time

show profiles;

• Modify table structure ( Add index )

ALTER table tableName ADD INDEX indexName(columnName)
ALTER TABLE create_index ADD INDEX name_index(NAME(10))

unique index
   Similar to the previous normal index , The difference is that ： The value of the index column must be unique , But you can have an empty value . If it's a composite index , The combination of column values must be unique . There are several ways to create it ：

• Create unique index

CREATE UNIQUE INDEX indexName ON mytable(username(length)) 
CREATE UNIQUE INDEX name_index2 ON create_index(name(10))

• Modify the table structure to create a unique index

ALTER table mytable ADD UNIQUE [indexName] (username(length));
ALTER TABLE create_index ADD UNIQUE name_index3(name(10));

• When creating a table, specify

CREATE TABLE create_index(  
ID INT NOT NULL,   
name VARCHAR(16) NOT NULL,  
UNIQUE [indexName] (username(length))  
);  

• Use ALTER Command add index

// There are four ways to add indexes to a data table ：
ALTER TABLE tbl_name ADD PRIMARY KEY (column_list):  This statement adds a primary key , This means that the index value must be unique , And cannot be NULL.
ALTER TABLE tbl_name ADD UNIQUE index_name (column_list):  The value of the index created by this statement must be unique （ except NULL Outside ,NULL There may be many times ）.
ALTER TABLE tbl_name ADD INDEX index_name (column_list):  Add a normal index , Index values can appear multiple times .
ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list): The statement specifies that the index is  FULLTEXT , For full-text indexing .

View

   For complex queries , Used in many places , If demand changes , You need to change sql sentence , It needs to be modified in multiple places , It's very troublesome to maintain .
solve ： Define views
The essence of view is the encapsulation of query , Define views , It is suggested that v_ start
grammar ：

create view  View name  as select sentence ;

• example ： Create view , Query students' corresponding score information

create view v_stu_score_course as
select
stu.*,cs.courseNo,cs.name courseName,sc.score
from
students stu
inner join scores sc on stu.studentNo = sc.studentNo
inner join courses cs on cs.courseNo = sc.courseNo

CREATE VIEW v_stu AS
SELECT
name,sex
FROM
students
// Use view 
SELECT * FROM v_stu

• View view ： The view table will list all the views as well

show tables;

• Delete view

drop view  View name ;
 example ：
drop view v_stu_score_course;

• Use view ： The purpose of a view is to query

select * from v_stu_score_course;
SELECT * FROM v_stu

stored procedure

   stored procedure （Stored Procedure） It's a complex program stored in a database , A database object that can be called by an external program . Stored procedures are designed to accomplish specific functions SQL Statements set , Compiled, created and stored in a database , The user can specify the name of the stored procedure and give the parameters ( When needed ) To call execution . Stored procedures are very simple in mind , Database SQL Language level code encapsulation and reuse .

advantage

• Stored procedures can be encapsulated , And hide complex business logic .
• Stored procedures can return values , And can accept parameters .
• Stored procedures cannot be used SELECT Command to run , Because it's a subroutine , And view table , Data tables or user-defined functions are different .
• Stored procedures can be used for data validation , Enforce business logic, etc .

shortcoming

• stored procedure , Often customized to a specific database , Because the supported programming languages are different . When switching to the database system of other manufacturers , You need to rewrite the original stored procedure .
• Performance tuning and writing of stored procedures , Limited by various database systems .
• grammar ：

delimiter $$
create procedure  Stored procedure name ( parameter list )
begin
sql sentence 
end$$
delimiter ;

• explain ： delimiter Used to set the separator , The default is semicolon
• analysis ： By default , Stored procedures are associated with the default database , If you want to specify that the stored procedure is created under a specific database , Then prefix the procedure name with the database name . When defining a process , Use DELIMITER $$ The command changes the closing symbol of a statement from a semicolon ; Temporarily changed to two $$, So that the semicolon used in the process body is passed directly to the server , Not by the client （ Such as mysql） explain .
• Example ：
  requirement ： Create query process , Search for student information
• step1： Set the separator

delimiter $$

• step2： Create stored procedure

create procedure proc_stu()
begin
select * from students;
end$$

• step3： Restore delimiter

delimiter ;

• Call syntax ：

call  stored procedure ( parameter list );
 Calling stored procedure proc_stu
call proc_stu();

function

• Create function syntax

delimiter $$
create function  The name of the function ( parameter list ) returns  Return type 
begin
sql sentence 
end
$$
delimiter ;

• Example of function
  requirement ： Create a function my_trim, Used to delete the spaces on the left and right sides of the string
• step1： Set the separator

delimiter $$

• step2： Create a function

create function my_trim(str varchar(100)) returns varchar(100)
begin
return ltrim(rtrim(str));
end
$$

• step3： Restore delimiter

delimiter ;

• Use custom functions

select ' abc ',my_trim(' abc ')

• summary ：
• Stored procedures and functions are designed to operate the database repeatedly sql Collection of statements .
• Stored procedures and functions are compiled at one time , It will be cached , The next time you use it, you will directly hit the compiled... In the cache sql, There is no need to compile repeatedly
• Reduce network interaction , Reduce network access traffic

Change Password

explain ： modify user The password of the table is the password of modifying the database

• Use root Sign in , modify mysql Database user surface
• Use password() Function for password encryption
• Note that the permissions need to be refreshed after modification

use mysql;
update user set password=password(' New password ') where user=' user name ';
 example ：
update user set password=password('123') where user='root';
 Refresh the permissions ： flush privileges;

forget root Account password
1、 To configure mysql You don't need a password to log in , Modify the configuration file

• Centos in ： The configuration file location is /data/server/mysql/my.cnf
• Windows in ： The configuration file location is C:\Program Files (x86)\MySQL\MySQL Server 5.1\my.ini modify , find mysqld, On the next line , add to skip-grant-tables

[mysqld]
skip-grant-tables

2、 restart mysql, Password free login , modify mysql Database user surface

use mysql;
update user set password=password(' New password ') where user=' user name ';
 example ：
update user set password=password('123') where user='root';
 Refresh the permissions ： flush privileges;

3、 Restore profile , Just add the skip-grant-tables Delete , restart