Detailed explanation of MySQL index: Understand the role and usage of unique index

Detailed explanation of MySQL index: Understand the role and usage of unique index

In the database, the index is a data structure that can speed up data retrieval. In MySQL, index is a very important data structure that can help us retrieve data more efficiently. This article will focus on unique indexes, explain the role and usage of unique indexes in detail, and provide specific code examples to help readers better understand the concept of unique indexes.

What is a unique index?

In MySQL, unique index is an index type. Its function is to ensure that the value in the index column is unique, that is, each value can only appear once. Different from ordinary indexes, unique indexes require that the value in the indexed column be unique in the entire table and allow the occurrence of NULL values.

The role of unique index

1. Ensure uniqueness: The unique index can ensure that the value in the indexed column is unique, avoiding Duplicate data appears to ensure the uniqueness of the data.
2. Improve retrieval speed: Because unique indexes can help the database quickly locate the data that needs to be retrieved, it can speed up data retrieval and improve query efficiency.
3. Avoid the insertion of redundant data: Use unique indexes to avoid inserting duplicate data and improve the data integrity of the database.

Usage of unique index

In MySQL, we can specify a unique index when creating a table, or add a unique index to an existing table. . The following will illustrate the usage of unique index through specific code examples.

Specify unique index when creating the table

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) UNIQUE,
    email VARCHAR(100) UNIQUE,
    ...
);

In the above example, when we created the users table, we added unique indexes to the username and email columns respectively to ensure the uniqueness of username and email.

Add unique index on existing table

CREATE UNIQUE INDEX idx_username ON users(username);

Through the above code, we have A unique index named idx_username is added to the users table to ensure the uniqueness of the username column.

Note

1. When a unique index is added to the table, if you try to insert duplicate data, MySQL will throw an error and refuse to insert duplicate data. data.
2. When there is already data in the table, adding a unique index may involve uniqueness constraints on the data. Therefore, before adding a unique index, you need to ensure the uniqueness of the data.

Through the introduction of this article, I believe that readers will have a deeper understanding of the concept, function and usage of unique indexes. In the actual database design and use process, reasonable use of unique indexes can improve database performance, ensure data integrity, and help us manage data more efficiently. I hope that readers can better apply unique indexes to actual database projects after reading this article.

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