"Obe, Regina" <robe.dnd@xxxxxxxxxxxxxxxx> writes: > Does PostgreSQL use the COMMUTATOR property of an operator to determine > if flip-flopped arguments can be collapsed. No. In recent releases we don't even bother to look for simple duplicate clauses (it's seldom worth the cycles), let alone clauses that would be duplicates after some transformation or other. > I used to think it did until someone pointed it doesn't - For example > in the below > SELECT b.* > FROM boszip b INNER JOIN landparcels l > ON (b.the_geom && l.the_geom AND l.the_geom && b.the_geom AND > l.the_geom && b.the_geom ) > WHERE l.gid = b.gid and b.gid = l.gid > limit 1 > If I look at the query plan - I see the plan has reduced things down to > l.gid = b.gid AND (b.the_geom && l.the_geom AND l.the_geom && > b.the_geom) 8.3 will do that (prior releases will often fail to recognize the redundancy) but it's an outgrowth of mergejoin equivalence-class processing. && isn't a mergejoinable equality operator so nothing much happens to those clauses. regards, tom lane
