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)
);

In the above code,

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

In addition to specifying indexes when creating the table, you can also add indexes by modifying the table structure. For example, the sample code to add an index to the

age column of the existing users table is as follows:

ALTER TABLE users ADD INDEX idx_age (age);

In the above code,

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.

4. How to use index?

When there is an index in the table, you can use the index to quickly query data through the

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;

In the above code,

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.

5. How to optimize the use of indexes?

Correct selection and use of indexes is the key to improving query performance. Here are some suggestions for optimizing index usage:

Thin Index

Excessive indexes increase maintenance overhead and may cause performance degradation. Create only necessary indexes and avoid creating redundant or duplicate indexes.

Use index coverage query

Index coverage query means that the columns in the query statement are included in the index, so that the query can directly use the data in the index without You need to find the original data row again. By reducing IO operations, query efficiency can be improved.

Pay attention to the order of index columns

When creating a composite index, the order of index columns is important. Usually the most commonly used columns are placed first to improve query efficiency.

Avoid calculation or conversion of index columns

Computation or conversion of index columns will cause MySQL to be unable to use the index for queries. Even if indexes are used, additional overhead will be added. Therefore, try to avoid calculations or conversions on index columns.

Summary:

The creation and use of indexes are important means to optimize query performance in MySQL. By creating appropriate indexes and correctly using indexes for queries, query efficiency can be greatly improved. However, excessive or incorrect use of indexes can also lead to performance degradation. Therefore, when using indexes, optimization and adjustments need to be made according to specific circumstances.

(Note: The above example code is for demonstration purposes only. Please modify it appropriately according to the actual situation when using it)

References:

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

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