Advanced learning of MySQL -- Application -- index

install Linux Version of mysql

System : centOS7
msyql: 8.0.26

Index Overview

An index is an ordered data structure
Can help MySQL Efficient data acquisition .

That means : In the database table structure , In addition to saving data , The database also needs to maintain the data structure of index , Use these structures to point to the saved data . In this way, advanced search algorithms can be used in these data structures , Quickly locate the original data .

Index structure

MySQL The index of is implemented in the storage engine layer , Different storage engines have different structures , It mainly includes the following :

Binary tree index structure

improvement :

B-tree Index structure

Take a maximum degree as 5 Of b-tree For example ( Each node can store up to 4 individual key, 5 A pointer to the )

B+tree Index structure

All elements are only in leaf nodes , Those above are just for indexing .
Leaf nodes form a one-way linked list .

Hash Index structure

hsah Features of index :
It can only be used for peer-to-peer comparison , Range query is not supported ;
Cannot sort with index ;
Query efficiency is higher than B+tree;

stay mysql in , Support hash The indexing engine is , memory engine , and InnoDB It has adaptive function hash function , hash The index is the storage engine B+tree Automatically built under specified conditions .

Why B+tree

Index classification

Summary

You can find , Innodb Even if the table stores more than 20 million records , It's only three floors . Efficiency is very high .
If there are hundreds of millions of records , Then we have to consider the sub database and sub table ~

Index Syntax

SQL Performance analysis

Index usage

Index design principles