search
HomeDatabaseMysql Tutorialmysql 索引分类以及用途分析

MySQL索引分为普通索引、唯一性索引、全文索引、单列索引、多列索引等等。这里将为大家介绍着几种索引各自的用途。

一、 MySQL: 索引以B树格式保存

  Memory存储引擎可以选择Hash或BTree索引,Hash索引只能用于=或的等式比较。

  1、普通索引:create index on Tablename(列的列表)

  alter table TableName add index (列的列表)

  create table TableName([...], index [IndexName] (列的列表)

  2、唯一性索引:create unique index

  alter ... add unique

  主键:一种唯一性索引,必须指定为primary key

  3、全文索引:从3.23.23版开始支持全文索引和全文检索,FULLTEXT,

  可以在char、varchar或text类型的列上创建。

  4、单列索引、多列索引:

  多个单列索引与单个多列索引的查询效果不同,因为:

  执行查询时,MySQL只能使用一个索引,会从多个索引中选择一个限制最为严格的索引。

  5、最左前缀(Leftmost Prefixing):多列索引,例如:fname_lname_age索引,以下的搜索条件MySQL都将使用

  fname_lname_age索引:firstname,lastname,age;firstname,lastname;firstname,其他情况将不使用。

二、根据sql查询语句确定创建哪种类型的索引,如何优化查询

  选择索引列:

  a.性能优化过程中,选择在哪个列上创建索引是最重要的步骤之一。可以考虑使用索引的主要有

  两种类型的列:在where子句中出现的列,在join子句中出现的列。

  b.考虑列中值的分布,索引的列的基数越大,索引的效果越好。

  c.使用短索引,如果对字符串列进行索引,应该指定一个前缀长度,可节省大量索引空间,提升查询速度。

  d.利用最左前缀

  e.不要过度索引,只保持所需的索引。每个额外的索引都要占用额外的磁盘空间,并降低写操作的性能。

  在修改表的内容时,索引必须进行更新,有时可能需要重构,因此,索引越多,所花的时间越长。

  MySQL只对一下操作符才使用索引:,>=,between,in,

  以及某些时候的like(不以通配符%或_开头的情形)。

mysql 索引分类

在数据库表中,对字段建立索引可以大大提高查询速度。通过善用这些索引,可以令 MySQL的查询和运行更加高效。索引是快速搜索的关键。MySQL索引的建立对于MySQL的高效运行是很重要的。下面介绍几种常见的MySQL索引类型。
1、普通型索引
这是最基本的索引类型,而且它没有唯一性之类的限制。普通索引可以通过以下几种方式创建:
(1)创建索引,例如CREATE INDEX 索引的名字 ON tablename (列名1,列名2,...);
(2)修改表,例如ALTER TABLE tablename ADD INDEX 索引的名字 (列名1,列名2,...);
(3)创建表的时候指定索引,例如CREATE TABLE tablename ( [...], INDEX 索引的名字 (列名1,列名
2,...) );
2、唯一索引
这种索引和前面的“普通索引”基本相同,但有一个区别:索引列的所有值都只能出现一次,即必须唯一。唯一性索引可以用以下几种方式创建:
(1)创建索引,例如CREATE UNIQUE INDEX 索引的名字 ON tablename (列的列表);
(2)修改表,例如ALTER TABLE tablename ADD UNIQUE 索引的名字 (列的列表);
(3)创建表的时候指定索引,例如CREATE TABLE tablename ( [...], UNIQUE 索引的名字 (列的列
表) );
3、主键
主键是一种唯一性索引,但它必须指定为“PRIMARY KEY”。如果你曾经用过AUTO_INCREMENT类型的列,你可能已经熟悉主键之类的概念了。主键一般在创建表的时候指定,例如“CREATE TABLE tablename ( [...], PRIMARY KEY (列的列表) ); ”。但是,我们也可以通过修改表的方式加入主键,例如“ALTER TABLE tablename ADD PRIMARY KEY (列的列表); ”。每个表只能有一个主键。 (主键相当于聚合索引,是查找最快的索引)
4、单列索引和多列索引
索引可以是单列索引,也可以是多列索引。
(1)单列索引就是常用的一个列字段的索引,常见的索引。
(2)多列索引就是含有多个列字段的索引
alter table student add index sy(name,age,score);
索引sy就为多列索引,多列索引在以下几中情况下才能有效:
select * from student where name='jia' and age>='12' //where条件中含有索引的首列字段和
第二个字段
select * from student where name='jia' //where条件中只含有首列字段
select * from student where name='jia' and score段
总结:多列索引只有在where条件中含有索引中的首列字段时才有效
5、选择索引列
应该怎样选择索引列,首先要看查询条件,一般将查询条件中的列作为索引
Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Reduce the use of MySQL memory in DockerReduce the use of MySQL memory in DockerMar 04, 2025 pm 03:52 PM

This article explores optimizing MySQL memory usage in Docker. It discusses monitoring techniques (Docker stats, Performance Schema, external tools) and configuration strategies. These include Docker memory limits, swapping, and cgroups, alongside

How to solve the problem of mysql cannot open shared libraryHow to solve the problem of mysql cannot open shared libraryMar 04, 2025 pm 04:01 PM

This article addresses MySQL's "unable to open shared library" error. The issue stems from MySQL's inability to locate necessary shared libraries (.so/.dll files). Solutions involve verifying library installation via the system's package m

How do you alter a table in MySQL using the ALTER TABLE statement?How do you alter a table in MySQL using the ALTER TABLE statement?Mar 19, 2025 pm 03:51 PM

The article discusses using MySQL's ALTER TABLE statement to modify tables, including adding/dropping columns, renaming tables/columns, and changing column data types.

Run MySQl in Linux (with/without podman container with phpmyadmin)Run MySQl in Linux (with/without podman container with phpmyadmin)Mar 04, 2025 pm 03:54 PM

This article compares installing MySQL on Linux directly versus using Podman containers, with/without phpMyAdmin. It details installation steps for each method, emphasizing Podman's advantages in isolation, portability, and reproducibility, but also

What is SQLite? Comprehensive overviewWhat is SQLite? Comprehensive overviewMar 04, 2025 pm 03:55 PM

This article provides a comprehensive overview of SQLite, a self-contained, serverless relational database. It details SQLite's advantages (simplicity, portability, ease of use) and disadvantages (concurrency limitations, scalability challenges). C

Running multiple MySQL versions on MacOS: A step-by-step guideRunning multiple MySQL versions on MacOS: A step-by-step guideMar 04, 2025 pm 03:49 PM

This guide demonstrates installing and managing multiple MySQL versions on macOS using Homebrew. It emphasizes using Homebrew to isolate installations, preventing conflicts. The article details installation, starting/stopping services, and best pra

How do I configure SSL/TLS encryption for MySQL connections?How do I configure SSL/TLS encryption for MySQL connections?Mar 18, 2025 pm 12:01 PM

Article discusses configuring SSL/TLS encryption for MySQL, including certificate generation and verification. Main issue is using self-signed certificates' security implications.[Character count: 159]

What are some popular MySQL GUI tools (e.g., MySQL Workbench, phpMyAdmin)?What are some popular MySQL GUI tools (e.g., MySQL Workbench, phpMyAdmin)?Mar 21, 2025 pm 06:28 PM

Article discusses popular MySQL GUI tools like MySQL Workbench and phpMyAdmin, comparing their features and suitability for beginners and advanced users.[159 characters]

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
2 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Repo: How To Revive Teammates
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
Hello Kitty Island Adventure: How To Get Giant Seeds
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment