What is a clustered index in mysql

Clustered index is an algorithm that reorganizes the actual data on disk to sort by the value of one or more specified columns. The characteristics of a clustered index are: the order of storing data is consistent with the order of the index, the primary key will create a clustered index by default, and only one clustered index is allowed to exist in a table.

Clustered index

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Clustered index is an algorithm that reorganizes the actual data on disk to sort by the value of one or more specified columns.

Features:

The order of stored data is consistent with the index order.

Generally, the primary key will create a clustered index by default, and only one clustered index is allowed to exist in a table (reason: once the data is stored, there can only be one order).

The difference between clustered index and non-clustered index is explained in the book "Database Principles":

The leaf nodes of the clustered index are the data nodes. , the leaf nodes of the non-clustered index are still index nodes, but have pointers to the corresponding data blocks.

Advantages and disadvantages of clustered index:

Advantage: When there are relatively few query entries according to the primary key, there is no need to go back (the data is under the primary key node).

Disadvantages: If irregular data is inserted, frequent page splits will occur.

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