A detailed introduction to the index length issue of MySQL indexes
The length of the index created in each single table of MySQL is limited, and there are different restrictions on tables under different storage engines.
In the MyISAM table, when creating a combined index, the length of the created index cannot exceed 1000. Note that the calculation of the length of the index here is based on the length set by the table field. For example:
create table test(id int,name1 varchar(300),name2 varchar(300),name3 varchar(500))charset=latin1 engine=myisam; create index test_name on test(name1,name2,name3);
At this time, an error message is reported:
Specified key was too long;max key length is 1000 bytes.
Modify the table structure:
alter table test convert to charset utf8; create index test_name3 on test(name3).
At this time warning:
Specified key was too long;max key length is 1000 bytes.
But the index is created successfully. Looking at the table structure, you can see that the created index is a prefix index:
‘key test_name3(name3(333))’
The conclusion is: for the myisam table, if you create a combined index, the sum of the lengths of the created indexes cannot exceed 1000 bytes, otherwise an error will be reported , the creation failed; for myisam's single-column index, the maximum length cannot exceed 1000, otherwise an alarm will occur, but the creation is successful, and the final creation is a prefix index (the first 333 bytes are taken).
In the Innodb table, create a composite index:
create table test1(id int,name1 varchar(300),name2 varchar(300),name3 varchar(500))charset=latin1 engine=innodb; create index test1_name on test(name1,name2,name3);
At this time, is given
warning:Specified key was too long;max key length is 767 bytes.
Modify the table structure:
alter table test1 convert to charset utf8; create index test1_name3 on test(name3).
At this time,
warning:Specified key was too long;max key length is 767 bytes.
is given. The conclusion is: for creating a combined index in innodb, if the length of each column does not exceed 767, the total length of all columns will no longer be calculated. If there is more than 767, an alarm will be given. The index will be created successfully in the end, but for more than 767 The column of bytes takes the prefix index; for the single-column index of InnoDB, if it exceeds 767, a warning is given. In the end, the index is created successfully, and the prefix index is taken (the first 255 bytes are taken).
The above is the detailed introduction to the index length issue of MySQL index. For more related content, please pay attention to the PHP Chinese website (www.php .cn)!

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

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

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.

MySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen

MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.

Apache connects to a database requires the following steps: Install the database driver. Configure the web.xml file to create a connection pool. Create a JDBC data source and specify the connection settings. Use the JDBC API to access the database from Java code, including getting connections, creating statements, binding parameters, executing queries or updates, and processing results.

The process of starting MySQL in Docker consists of the following steps: Pull the MySQL image to create and start the container, set the root user password, and map the port verification connection Create the database and the user grants all permissions to the database

The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.

The key to installing MySQL elegantly is to add the official MySQL repository. The specific steps are as follows: Download the MySQL official GPG key to prevent phishing attacks. Add MySQL repository file: rpm -Uvh https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm Update yum repository cache: yum update installation MySQL: yum install mysql-server startup MySQL service: systemctl start mysqld set up booting

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.
