I wish to do an HQL query on 2 tables where the columns are not related by a primary or foreign key. One of the tables holds denormalised data, and is not constrained by anything on the database. I merely want to join my first table onto this, but I'm not sure how to define the field mappings in this scenario.

it is very hard to work with denormalized tables and arbitrary join criteria so I would sugest you not to attempt to map that table but to use a plain SQL query instead.

cheers,
radu