Is the primary key automatically indexed in MySQL?
According to http://dev.mysql.com/doc/refman/5.0/en/constraint-primary-key.html it would appear that this is would be implicit
Even though this was asked in 2009 figured I'd post an actual reference to the MySQL documentation on primary keys.http://dev.mysql.com/doc/refman/5.5/en/optimizing-primary-keys.html
The primary key for a table represents the column or set of columns that you use in your most vital queries. It has an associated index, for fast query performance
For MySQL 5.0 reference see: http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html
Most MySQL indexes (PRIMARY KEY, UNIQUE, INDEX, and FULLTEXT) are stored in B-trees. Exceptions are that indexes on spatial data types use R-trees, and that MEMORY tables also support hash indexes.