Advantages and usage of prefix index in MySQL

Advantages and usage of prefix index in MySQL

In the MySQL database, indexing is one of the important means to improve query efficiency. In addition to the common full-field index, there is also a special index called a prefix index. This article will introduce the advantages and usage of prefix indexes, with specific code examples.

1. What is a prefix index

The prefix index only indexes the first few characters of the field, not the entire field content. The advantage of this is that it can save index storage space, increase index creation speed, and improve query performance in some specific scenarios.

2. Advantages of prefix index

• Save storage space: Compared with full field index, prefix index only saves the field information part of the content, so it takes up less storage space.
• Increase index creation speed: As the index size is reduced, the speed of index creation is also increased accordingly.
• Optimize specific queries: For some specific types of queries, prefix indexes may be more suitable and can improve query performance.

3. Usage of prefix index

The following will demonstrate the usage of prefix index through a specific table and code example.

Suppose there is a table named users, which contains the name field, and we want to create a prefix index for the name field.

First, create the users table:

CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(100)
);

Then, create a prefix index for the name field, indexing only the first 5 characters:

CREATE INDEX idx_name ON users (name(5));

Next, we can verify the creation of the index through the following query:

EXPLAIN SELECT * FROM users WHERE name LIKE 'John%';

The execution plan of the query can be viewed through the EXPLAIN keyword to ensure that the prefix index is correctly application.

4. Notes

When using prefix index, you need to pay attention to the following points:

• Choose the appropriate prefix Length: The prefix length should not be too long. The appropriate length needs to be selected according to the specific scenario and data distribution.
• Not applicable to all situations: Prefix index is not applicable to all situations. You need to judge whether to use prefix index based on actual needs and query characteristics.

5. Summary

Prefix index is an important index type in MySQL. By only indexing the first few characters of the field, you can save storage space, improve index creation speed, and optimize query performance in specific scenarios. In actual applications, you need to decide whether to use a prefix index according to the specific situation, and pay attention to choosing an appropriate prefix length.

The above is an introduction to the advantages and usage of prefix indexes in MySQL. I hope it will be helpful to readers.

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