Analysis of the principle of prefix index in MySQL

Principle analysis and code examples of prefix index in MySQL

Prefix index is a technology for optimizing query performance in MySQL database, by only performing part of the field value Index to reduce the size of the index, thereby improving query efficiency. This article will analyze the principle of prefix index in detail and provide specific code examples to help readers better understand.

Prefix index principle analysis

In MySQL, ordinary indexes sort and store the entire field value. But when the field value is very long, such as VARCHAR (255) type, this will cause the size of the index to become very large, thus reducing the efficiency of the index. The prefix index can solve this problem. It only indexes the specific length of the field value instead of the entire field value.

When creating a prefix index, MySQL will only store the specified length of the field value, rather than the entire value. This reduces the size of the index and improves query efficiency. However, it should be noted that using prefix indexes may result in inaccurate query results because only part of the field value is indexed.

Example of creating a prefix index

Suppose there is a table named users, in which there is a username field that needs to be created as a prefix index. The following is a sample SQL code that shows how to create a prefix index:

ALTER TABLE users ADD INDEX idx_username(username(10));

In the above code, idx_username is the name of the index, and username is the index to be created Field name, (10) means that only the first 10 characters of the field value are indexed. Creating a prefix index in this way can effectively reduce the size of the index and improve query efficiency.

How to use prefix index when querying

When using prefix index to query, you need to ensure that the query conditions also use prefixes of the same length. Otherwise, MySQL cannot effectively utilize the index, resulting in reduced query efficiency.

The following is an example SQL code that shows how to use the prefix index when querying:

SELECT * FROM users WHERE username LIKE 'john%';

In the above query, the prefix index for the username field can be effectively Improve query efficiency because the query conditions also start with a prefix of the same length.

Summary

Through the introduction of this article, readers should have a deeper understanding of the principles of prefix indexes in MySQL. Prefix index is a technology for optimizing query performance, which can help reduce the size of the index and improve query efficiency. However, when using prefix indexes, you need to pay attention to the matching length of the query conditions to avoid affecting the accuracy of the query results. I hope readers can better understand and apply prefix index technology through the content of this article.

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