Markus, Well this is just a guess on my part. ST_Within() is the standards compliant named one. Within() is obsolete by standards as well (even though you are right most spatial databases never needed that extra annoying && be added).
The reason I believe Within() was not made to behave exactly like ST_Within() is for reverse-compatibility. e.g. b && a AND ST_Within(a,b) is slightly slower than b && a AND Within(a,b) Because the postgres optimizer does not make the distinction that a && b is the same as b && a --> although it would realize that a && b AND a && b -> a && b so lets say you had code like this b && a AND Within(a,b) and the behavior of Within was changed to a && b AND _ST_Within(a,b) Then your old code would suddenly expand to b && a AND a && b AND _ST_Within(a,b) Which is slower than what you had before. I asked this on the PostgreSQL general list before that why doesn't Postgres use the commutator property of an operator to collapse b && a and a && b -> a && b Tom Lane replied and he said from a planner standpoint, the extra cycles it would add to planning would be more than the gain in most cases. http://archives.postgresql.org/pgsql-general/2008-04/msg00647.php There are similar things about the new function cost thing I find annoying and don't behave as intuitively as I would like for the same reason. http://archives.postgresql.org/pgsql-general/2008-02/msg01224.php Hope that helps, Regina -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Markus Schaber Sent: Thursday, June 05, 2008 5:40 AM To: [email protected] Subject: Re: [postgis-users] GIST index speed Hi, Kevin, Kevin Neufeld <[EMAIL PROTECTED]> wrote: > Are you using within() or ST_Within()? The latter automatically uses the > gist index, the former does not. As I was absent from the lists for some time, why was this distinction introduced? Normally, I would expect the standards compliant version to be optimizable by the query planner. Regards, Markus -- Markus Schaber | Logical Tracking&Tracing International AG Dipl. Inf. | Software Development GIS Fight against software patents in Europe! www.ffii.org www.nosoftwarepatents.org _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users ----------------------------------------- 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. _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
