Are primary keys automatically indexed in MySQL?

Yes, primary keys are automatically indexed in MySQL because primary keys, indexes, etc. are stored in B-trees. All engines including InnoDB and MyISAM automatically support primary key indexes.

Primary keys are implicitly indexed in InnoDB, MyISAM, and other engines.

Let’s create a table with a primary key -

mysql> create table DemoIndex
   -> (
   -> Id int not null,
   -> primary key(Id)
   -> );
Query OK, 0 rows affected (1.21 sec)

In the above table, Id is implicitly indexed.

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