- ST_Distance returns NULL if the geometry value passed to it is the empty set.
Both geometries must use the same spatial reference system (have the same SRS ID).
- If a geospatial index is defined on the geospatial data column to which this method is applied, the index will only be used if method appears in the WHERE clause of a query such that the distance between the geometries is less than or equal to a constant. For example:
... WHERE geom.ST_Distance(otherGeom) < 10 ... WHERE 10 >= geom.ST_Distance(otherGeom)