Clustered index of the MySQL InnoDB storage engine

InnoDB Clustered Index

MySQL has no support for clustered indexes, depending on which storage engine is used.

MySQL InnoDB is bound to build a clustered index, so-called aggregation, refers to the actual data rows and related key values are saved in a piece, which also determines that a table can only have a clustered index , that is, MySQL does not save the data row in two places at a time. InnoDB are usually clustered according to the primary key value (primary key), but what happens when a table has no PK? InnoDB the order in which the clustered index reference columns are selected is:

1. If the primary key (primary key) is declared, the column will be made a clustered index
2. If no primary key is declared, a unique and non-empty index column is used as the primary key, which becomes the clustered index of this table
3. The above two conditions are not satisfied, InnoDB will generate a virtual clustered index on its own.