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This article mainly introduces the meaning of mysql coverage index, the article is very detailed, has a certain reference value, interested friends must read it!

1. The required columns in the query statement are in the index, so that the query results can be found in the data structure of the index.

2. Because the overlay index can reduce the search times of trees and significantly improve the query performance, the use of overlay index is a common performance optimization method.

Example

+-+-+ | 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 | +-+ -+-+ above is all the content of the article "what does the mysql coverage index mean?" Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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