STDistance (geography Data Type)
Returns the shortest distance between a point in a geography instance and a point in another geography instance.
STDistance() returns the shortest LineString between two geography types. This is a close approximate to the geodesic distance. The deviation of STDistance() on common earth models from the exact geodesic distance is no more than .25%. This avoids confusion over the subtle differences between length and distance in geodesic types.
STDistance() always returns null if the spatial reference IDs (SRIDs) of the geography instances do not match.
Methods of the geography data type that calculate an area or distance return different results based on the SRID of the instance used in the method. For more information on SRIDs, see Spatial Reference Identifiers (SRIDs).
DECLARE @g geography; DECLARE @h geography; SET @g = geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656)', 4326); SET @h = geography::STGeomFromText('POINT(-122.34900 47.65100)', 4326); SELECT @g.STDistance(@h);