Add in principle for MySQL index

MySQL index adding principles and code examples

1. Introduction
In the MySQL database, indexing is one of the important means to improve query efficiency and optimize database performance. . Adding indexes correctly can greatly reduce disk IO operations during query and improve query speed. However, when adding indexes, you need to follow some principles to ensure the effectiveness and performance improvement of the index. This article will introduce some common MySQL index adding principles and give specific code examples to help readers better understand and apply them.

2. Principles for adding indexes

1. Select appropriate columns as indexes
When selecting columns as indexes, you should give priority to columns that are often used in query conditions or join conditions. Generally speaking, primary key and foreign key columns are the columns most commonly used in queries and joins, so they are usually the most appropriate choice. In addition, some columns that are commonly used for sorting or grouping can also consider adding indexes.

2. Avoid unnecessary indexes
Although indexes can improve query efficiency, they will also increase the burden of write operations. Therefore, you should not add an index to every column, but choose based on actual needs. Adding an index is generally not suitable for columns that have only a small number of unique values, columns that are updated frequently, or columns that are long.

3. Add joint index for joint query
When we perform joint query, we can add joint index for columns that are often queried together to improve query efficiency. For example, for querying the student table and grade table, you can add a joint index for the two commonly used joint condition columns, student number and course number.

4. Pay attention to the order of the index
When adding a joint index, you need to pay attention to the order of the index fields. Typically, more selective columns should be placed first to improve query efficiency. A column with higher selectivity means that the column has more different values ​​and can filter out more data.

5. Add a prefix index to the string column
For longer string columns, in order to reduce the size of the index and improve query efficiency, you can choose to add a prefix index to the string column. By specifying the index length, the size and memory footprint of the index can be greatly reduced, thereby improving performance.

3. Code examples

1. Add an index to a single column

--Add an index to the student number column of the student table
ALTER TABLE students ADD INDEX idx_student_id (student_id );

2. Add a joint index for joint query

-- Add a joint index for the student number and course number columns of the student table and grade table
ALTER TABLE students ADD INDEX idx_student_course ( student_id, course_id);

IV. Summary
In the MySQL database, the correct use of indexes can greatly improve query efficiency and optimize database performance. When adding indexes, we need to select appropriate columns, avoid unnecessary indexes, add joint indexes for joint queries, pay attention to index order, and add prefix indexes for longer string columns. By following these principles, we can better utilize indexes to optimize database queries. At the same time, I hope that the code examples given in this article will be helpful to readers so that they can better understand and apply the relevant knowledge of MySQL indexes.

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