Create and utilize MySQL indexes

Creation and use of MySQL index

MySQL is a commonly used relational database management system used to store and manage data. Indexes are key to improving query performance when dealing with large amounts of data. This article will introduce how to create and use MySQL indexes and provide specific code examples.

1. What is an index?

An index is a data structure used to speed up the search for data in the database. It is similar to the table of contents of a book and can quickly locate the required data. The index in MySQL is implemented based on the B-tree data structure, and B-Tree indexes are usually used to improve query efficiency.

2. Why do you need an index?

In the absence of an index, the database needs to scan the entire table to find the required data, so the time complexity of the query will increase linearly as the amount of data increases. With the index, the database can directly locate the location containing the required data, greatly improving the efficiency of the query.

3. How to create an index?

1. Specify the index when creating the table

When creating the table, you can specify the index by adding keywords after the column definition. For example, create a table named users, which contains three columns: id, name, and age, and is id# The sample code for creating an index on the ## and name columns is as follows:

CREATE TABLE users (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  age INT,
  INDEX idx_id (id),
  INDEX idx_name (name)
);

INDEX idx_id (id) is expressed as the id column Create an index, INDEX idx_name (name) means creating an index for the name column. An index can be created for a specified column by using the INDEX keyword after the column definition.

Modify the table structure and add indexes

age column of the existing users table is as follows:

ALTER TABLE users ADD INDEX idx_age (age);

ALTER TABLE is used For modifying the table structure, ADD INDEX means adding an index, idx_age is the name of the index, and age is the column on which the index is to be created.

SELECT statement. For example, the sample code to query users who are 18 years or older in the users table is as follows:

SELECT * FROM users WHERE age >= 18;

WHERE is used to specify the query conditions, age >= 18 means to filter out users who are 18 years or older. MySQL will use indexes to quickly locate data that meets conditions.

Thin Index

Use index coverage query

Pay attention to the order of index columns

Avoid calculation or conversion of index columns

MySQL official documentation: https://dev.mysql.com/doc/
1. Network information: https://www.runoob.com/mysql/mysql-index.html

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