The Relational System - Mastering phpMyAdmin 3.1 for Effective MySQL Management - page 174

Our goal here is to create a relation between the book table (which contains the
author ID) and the author table (which describes each author by an ID). We start on
the Table view for the book table, go to Structure, and click the Relation view link.
Internal relations
As the book table is in MyISAM format, we see the following screen (otherwise, the
display would be different, as explained in the Foreign Key Relations section later):
This screen allows us to create Internal relations (stored in the pma_relation table)
because MySQL itself does not have any relational notion for MyISAM tables. The
empty drop-down list next to each column indicates that there are no relations (links)
to any foreign table.
Defining the relation
We can relate each field of the book table to a field in another table (or in the
same table, because self-referencing relations are sometimes necessary). The interface
finds both the unique and the non-unique keys in all the tables of the same database,
and presents the keys in drop-down lists. (Creating internal relations to other
databases from the interface is not currently supported.) The appropriate choice for
the author_id field is to select the corresponding author_id field from the author
table—also called defining the foreign key .