What is the mysql overlay index?
This article mainly explains "mysql coverage index is what", interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let Xiaobian take you to learn "what mysql coverage index is"!
The columns required in the query statement are in the index, so that the query results can be found in the data structure of the index.
Because coverage index can reduce the number of tree searches and significantly improve query performance, using coverage index is a common performance optimization method.
examples
+----+-------------+------------+------+-----------------------+--------------+---------+-------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+------------+------+-----------------------+--------------+---------+-------+------+-------------+| 1 | SIMPLE | user_group | ref | group_id,group_id_uid | group_id_uid | 4 | const | 5378 | Using index |+-----------------------Might as well do it! Here is the website, more related content can enter the relevant channels for inquiry, pay attention to us, continue to learn!
