Distance proximity: Use ST_DWithin not Distance
If you have a problem that involves finding the things within X distance of other things or finding what things
have nothing within X distance
do not use
ST_Distance for filtering and also do not try to use
ST_Intersects + ST_Buffer.
ST_DWithin instead. Why?
ST_DWithincan use an index and
ST_Bufferis just an approximation of a buffer and not an exact buffer
Also note that
ST_DWithin is supported for both geometry and geography.
We show examples using geography. Note geometry would use much the same except units are in the spatial reference units.
Finding closest things within 1609 meters (~1 mile)
1SELECT roads.road_name, pois.poi_name 2 FROM roads INNER JOIN pois 3 ON ST_DWithin(roads.geog, pois.geog, 1609);
Finding roads with nothing of interest within 1 mile.
We are using the fact that a LEFT JOIN returns null in the left table when no match is found
1SELECT roads.road_name, pois.poi_name 2 FROM roads LEFT JOIN pois 3 ON ST_DWithin(roads.geog, pois.geog, 1609) 4 WHERE pois.gid IS NULL;