Re: [GENERAL] Operator COMMUTATOR - how does postgresql use this information
"Obe, Regina" <[EMAIL PROTECTED]> 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 -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
[GENERAL] Operator COMMUTATOR - how does postgresql use this information
Does PostgreSQL use the COMMUTATOR property of an operator to determine if flip-flopped arguments can be collapsed. 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) Why is (b.the_geom && l.the_geom AND l.the_geom && b.the_geom) not reduced down to just b.the_geom && l.the_geom even though && is defined as the commutator of &&? Thanks, Regina - The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. It is intended solely for the addressee. If you received this in error, please contact the sender and delete the material from any computer.
