Home Backend Development PHP Tutorial MySQL Manual Version 5.0.20-MySQL Optimization (2) (1) (3)_PHP Tutorial

MySQL Manual Version 5.0.20-MySQL Optimization (2) (1) (3)_PHP Tutorial

Jul 13, 2016 pm 05:03 PM
mysql Same different two optimization manual scanning Version of type index connect



The connection type is the same as ALL, except that it only scans the index tree. It is usually faster than ALL because index files are usually smaller than data files. MySQL uses this join type in situations where the queried field knowledge is part of a separate index.


ALL


will do a full scan of the table to join with the records obtained from the previous table. At this point it would be bad if the first table was not marked as const, which is usually very bad in other situations. Normally, ALL can be avoided by adding indexes to retrieve records from the table faster.


possible_keys


The possible_keys field refers to which index MySQL may use when searching for table records. Note that this field is completely independent of the table order displayed by EXPLAIN. This means that the indexes contained in possible_keys may not be used in actual use. If the value of this field is NULL, it means that no index is used. In this case, you can check which fields in the WHERE clause are suitable for adding indexes to improve query performance. That's it, create the index and then check it with EXPLAIN. See chapter "14.2.2 ALTER TABLE Syntax" for details. If you want to see what indexes the table has, you can run SHOW INDEX FROM tbl_name.


key


key field shows the index that MySQL actually uses. When no index is used, the value of this field is NULL. To force MySQL to use or ignore the index list in the possible_keys field, use the keywords FORCE INDEX, USE INDEX, or IGNORE INDEX in the query statement. For MyISAM and BDB type tables, you can use ANALYZE TABLE to help analyze which index is better to use. If it is a MyISAM type table, running the command myisamchk --analyze will have the same effect. For details, please see chapters "14.5.2.1 ANALYZE TABLE Syntax" and "5.7.2 Table Maintenance and Crash Recovery".


key_len


key_len field shows the length of the index used by MySQL. When the value of the key field is NULL, the length of the index is NULL. Note that the key_len value tells you which indexes MySQL will actually use in the joint index.

www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/630971.htmlTechArticleThe connection type is the same as ALL, but the difference is that it only scans the index tree. It is usually faster than ALL because index files are usually smaller than data files. MySQL has a separate index for the queried field knowledge...
Statement of this Website
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

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

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Roblox: Bubble Gum Simulator Infinity - How To Get And Use Royal Keys
1 months ago By 尊渡假赌尊渡假赌尊渡假赌
Nordhold: Fusion System, Explained
1 months ago By 尊渡假赌尊渡假赌尊渡假赌
Mandragora: Whispers Of The Witch Tree - How To Unlock The Grappling Hook
4 weeks ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

Java Tutorial
1677
14
PHP Tutorial
1280
29
C# Tutorial
1257
24
Laravel Introduction Example Laravel Introduction Example Apr 18, 2025 pm 12:45 PM

Laravel is a PHP framework for easy building of web applications. It provides a range of powerful features including: Installation: Install the Laravel CLI globally with Composer and create applications in the project directory. Routing: Define the relationship between the URL and the handler in routes/web.php. View: Create a view in resources/views to render the application's interface. Database Integration: Provides out-of-the-box integration with databases such as MySQL and uses migration to create and modify tables. Model and Controller: The model represents the database entity and the controller processes HTTP requests.

MySQL and phpMyAdmin: Core Features and Functions MySQL and phpMyAdmin: Core Features and Functions Apr 22, 2025 am 12:12 AM

MySQL and phpMyAdmin are powerful database management tools. 1) MySQL is used to create databases and tables, and to execute DML and SQL queries. 2) phpMyAdmin provides an intuitive interface for database management, table structure management, data operations and user permission management.

MySQL vs. Other Programming Languages: A Comparison MySQL vs. Other Programming Languages: A Comparison Apr 19, 2025 am 12:22 AM

Compared with other programming languages, MySQL is mainly used to store and manage data, while other languages ​​such as Python, Java, and C are used for logical processing and application development. MySQL is known for its high performance, scalability and cross-platform support, suitable for data management needs, while other languages ​​have advantages in their respective fields such as data analytics, enterprise applications, and system programming.

Laravel framework installation method Laravel framework installation method Apr 18, 2025 pm 12:54 PM

Article summary: This article provides detailed step-by-step instructions to guide readers on how to easily install the Laravel framework. Laravel is a powerful PHP framework that speeds up the development process of web applications. This tutorial covers the installation process from system requirements to configuring databases and setting up routing. By following these steps, readers can quickly and efficiently lay a solid foundation for their Laravel project.

Explain the purpose of foreign keys in MySQL. Explain the purpose of foreign keys in MySQL. Apr 25, 2025 am 12:17 AM

In MySQL, the function of foreign keys is to establish the relationship between tables and ensure the consistency and integrity of the data. Foreign keys maintain the effectiveness of data through reference integrity checks and cascading operations. Pay attention to performance optimization and avoid common errors when using them.

Compare and contrast MySQL and MariaDB. Compare and contrast MySQL and MariaDB. Apr 26, 2025 am 12:08 AM

The main difference between MySQL and MariaDB is performance, functionality and license: 1. MySQL is developed by Oracle, and MariaDB is its fork. 2. MariaDB may perform better in high load environments. 3.MariaDB provides more storage engines and functions. 4.MySQL adopts a dual license, and MariaDB is completely open source. The existing infrastructure, performance requirements, functional requirements and license costs should be taken into account when choosing.

What software is better for yi framework? Recommended software for yi framework What software is better for yi framework? Recommended software for yi framework Apr 18, 2025 pm 11:03 PM

Abstract of the first paragraph of the article: When choosing software to develop Yi framework applications, multiple factors need to be considered. While native mobile application development tools such as XCode and Android Studio can provide strong control and flexibility, cross-platform frameworks such as React Native and Flutter are becoming increasingly popular with the benefits of being able to deploy to multiple platforms at once. For developers new to mobile development, low-code or no-code platforms such as AppSheet and Glide can quickly and easily build applications. Additionally, cloud service providers such as AWS Amplify and Firebase provide comprehensive tools

SQL vs. MySQL: Clarifying the Relationship Between the Two SQL vs. MySQL: Clarifying the Relationship Between the Two Apr 24, 2025 am 12:02 AM

SQL is a standard language for managing relational databases, while MySQL is a database management system that uses SQL. SQL defines ways to interact with a database, including CRUD operations, while MySQL implements the SQL standard and provides additional features such as stored procedures and triggers.

See all articles