Mysql database indexing tutorial (super detailed)

Index preliminary

MySQL The establishment of index for MySQL It is very important to run efficiently , The index can be greatly

Improve MySQL Retrieval speed of

.

Take the catalog page of the Chinese Dictionary （ Indexes ） Let's say , We can press Pinyin 、 stroke 、 A catalogue sorted by radicals, etc （ Indexes ） Quickly find the words you need .

The index is divided into single column indexes 、 unique index 、 Composite index . Single index , That is, an index contains only a single column , A table can have multiple single-column indexes ; unique index , That is, the value of the index column must be unique , But you can have an empty value .  When you create a primary key, you will automatically create a unique 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 .

shortcoming

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 .

Index structure

Experiment preparation （ The following experiments are VMware In the middle of ）

1 platform MySQL host （5.7）

Prepare to write a 2 About ten million data sheets （ Of course not handwritten ）

Create index ：

Navicat 15 for MySQL

 ( Graphic tool )

1、 Create a new database

create database test default character set utf8; 


2、 Create a new data table

CREATE TABLE testsql (
 id int NOT NULL AUTO_INCREMENT PRIMARY KEY comment ' Since the primary key ',
 dept tinyint not null comment ' department id',
 name varchar(30) comment ' User name ',
 create_time datetime not null comment ' Registration time ',
 last_login_time datetime comment ' Last login time ' 
) comment ' The test table ';


3、 Write data

insert into testsql values(1,1,'user_1', '2018-01-01 00:00:00', '2018-03-01 12:00:00');


4、 assignment

set @i=1;


5、 Make a table with multiple increase （ Otherwise, tens of millions of data can't be written in a year ）

insert into testsql(dept, name, create_time, last_login_time) 
select left(rand()*10,1) as dept, # Random generation 1~10 The integer of
 concat('user_',@i:[email protected]+1), # Generate different... In sequence name
 date_add(create_time,interval [email protected]*cast(rand()*100 as signed) SECOND), # Generate random registration time with time sequence
 date_add(date_add(create_time,interval [email protected]*cast(rand()*100 as signed) SECOND), interval + cast(rand()*1000000 as signed) SECOND) # Generate a random last login time with a time sequence
from testsql;


Keep repeating the above command

The speed to the back will be slower and slower , It may take a few minutes , This is normal

6、 see

select count(*) from testsql;


This line of command can check how many columns the data table has reached

Until there are tens of millions of lines of numbers, you can stop

（ The effect can be seen in millions of lines ）

Check the log

show variables like "%_buffer%";


7、 experiment

At this time, the data table has reached tens of millions. You can query a row in the following tens of millions of data

select COUNT(*) from t where name='user_500000';


You can see that the search speed is very slow

8、 Create index

Select the data table , Right click the stand-alone button

You can choose any field to find the index name. My choice is name（ Others can be ）

Type I chose NORMAL, The method is BTREE

preservation , It may take a few minutes , Don't move at this time

9、 Experimental results

Search again at this time , You can see that the delay is gone

select COUNT(*) from t where name='user_500000';


That's all MySQL Tutorial of database indexing