A setting in the setup of the open catalog extension that you may be afraid to use, in that it might create a cartesian product using non-join's.
This feature is very useful if you want to join to a single row of a table but have no keys with which to do the join. Then the Cartesian product of 1 row with the rest of your results is exactly what you want. I have used this technique for joining some appropriate row of a currency conversion table and showing 2 values in a reports (USD and Euro, Canadian, etc)
