What is the concept of clustering index in MySQL?

A clustered index in MySQL is a special type of index that determines the physical storage order of data on disk. Unlike other types of indexes, a clustered index not only improves query performance but also reduces disk I/O operations.

A clustered index stores records in a table on disk in the order of the index key, so records with adjacent index keys are stored adjacent on disk as well. This storage method helps reduce random disk reads and improve query performance.

In MySQL, each table can only have one clustered index. Typically, the primary key is used as the clustered index because it is unique and does not allow null values. If a table does not have a defined primary key, MySQL will choose a unique and non-null index as the clustered index. If there are no suitable indexes in the table, MySQL will create a hidden clustered index that includes all columns in the table.

It is important to note that the creation of a clustered index will affect the performance of inserting and updating data in a table. This is because a clustered index determines the physical storage order of the data, so when inserting a new record, the appropriate position needs to be found based on the order of the index key. Similarly, updating operations also require adjusting the physical storage location of the data. Therefore, when designing table structures, it is necessary to balance the requirements of query performance and insertion/updating performance.