title: MySQL - clustered index on the "many" side of a "one to many" relationship
body: <p>I'm sure this is simple stuff to many of you, so I hope you can help easily.</p>
  
  <p>If I have a MySQL table on the "many" side of a "one to many" relationship - like this:</p>
  
  <pre><code>Create Table MyTable(
  ThisTableId int auto_increment not null,
  ForeignKey int not null,
  Information text
  )
  </code></pre>
  
  <p>Since this table would always be used via a join using ForeignKey, it would seem useful to make ForeignKey a clustered index so that foreign keys would always be sorted adjacently for the same source record. However, ForeignKey is not unique, so I gather that it is either not possible or bad practice to make this a clustered index? If I try and make a composite primary key using (ForeignKey, ThisTableId) to achieve both the useful clustering and uniqueness, then there is an error "There can only be one auto column and it must be defined as a key".</p>
  
  <p>I think perhaps I am approaching this incorrectly, in which case, what would be the best way to index the above table for maximum speed?</p>