Retus the distance based in two geo points (latitude/longitude)

haversine_geo_distance.sql

DELIMITER $$
CREATE FUNCTION haversine_geo_distance (lat1 REAL, lon1 REAL, lat2 REAL, lon2 REAL)
RETURNS REAL
BEGIN

	DECLARE RR LONG;
	DECLARE o1 REAL;
	DECLARE o2 REAL;
	DECLARE Ao REAL;
	DECLARE AA REAL;
	DECLARE a REAL;
	DECLARE c REAL;
	
	SET RR = 6371000;
	SET o1 = RADIANS(lat1);
	SET o2 = RADIANS(lat2);
	SET Ao = RADIANS(lat2 - lat1);
	SET AA = RADIANS(lon2 - lon1);
	
	SET a = SIN(Ao/2) * SIN(Ao/2) +
			COS(o1) * COS(o2) * 
			SIN(AA/2) * SIN(AA/2);
	SET c = 2 * ATAN2(SQRT(a), SQRT(1-a));
	RETURN RR * c;
	
END $$
DELIMITER ;