To ensure that such possibilities are not discarded the algorithm introduces the concept of interesting orders: an intermediate result has an interesting order if it is sorted by a final ORDER BY attribute,
GROUP BY attribute, or any attributes that participate in subsequent joins. For the above
example, the attributes c.clientNo, v.clientNo, v.propertyNo, and p.propertyNo are interesting.
During optimization, if any intermediate result is sorted on any of these attributes, then the
corresponding partial strategy must be included in the search.