Hi, So I have probably a simple question but I don't use PostGIS enough to know the right way to go about this. Hoping someone can help.
So I've got 3 spatial tables, each containing a bunch of polygon geometries. Let's call the tables A, B, C. What I want is to find out which polygons in table A are disjoint from all polygons in tables B and C. Meaning, which polygons in A have 0 overlap with polygons in B or C. I seem to have no troubles doing this when using only 2 tables, but adding the 3rd is messing things up. Oh, and I also want to invoke the GIST indexes to speed things up. Here's the (slightly generalized) query I think I should be using: SELECT <some stuff> FROM A, B, C WHERE disjoint(A.the_geom, B.the_geom) AND disjoint(A.the_geom, C.the_geom) AND <some other attribute filters> AND A.the_geom && B.the_geom AND A.the_geom && C.the_geom; I've not seen this query complete successfully as it takes so long, but I think something is wrong with it as running it against only A and B is really quick and there aren't too many geometries in the tables. Thoughts? Cheers, dylan _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
