 rel1.attr1=rel2.attr2</code>
     exists). Join pairs with no join clause are considered only when there
     is no other choice, that is, a particular relation has no available
     join clauses to any other relation. All possible plans are generated for
     every join pair considered by the planner, and the one that is
     (estimated to be) the cheapest is chosen.
    </p><p>
     When <code class="varname">geqo_threshold</code> is exceeded, the join
     sequences considered are determined by heuristi