Mysql How do you create a clustered index?

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According to Clustered and Secondary Indexes, you can have only one clustered index per table.

All indexes other than the clustered index are known as secondary indexes.

If a table has no primary index but another unique index, this is used as the clustered index.

If you do not define a PRIMARY KEY for your table, MySQL locates the first UNIQUE index where all the key columns are NOT NULL and InnoDB uses it as the clustered index.

So, I would conclude, that you don’t add a clustered index yourself, but MySQL chooses either the primary or the first unique index of a table as the clustered index.

If you haven’t defined a primary or unique index, MySQL creates an index itself

If the table has no PRIMARY KEY or suitable UNIQUE index, InnoDB internally generates a hidden clustered index named GEN_CLUST_INDEX on a synthetic column containing row ID values. The rows are ordered by the ID that InnoDB assigns to the rows in such a table. The row ID is a 6-byte field that increases monotonically as new rows are inserted. Thus, the rows ordered by the row ID are physically in insertion order.

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