mysql function to calculate distance between to earth points on a globe in kilometers

gistfile1.txt

DROP FUNCTION IF EXISTS distance;
DELIMITER $$
CREATE FUNCTION distance(lat1 FLOAT, lng1 FLOAT, lat2 FLOAT, lng2 FLOAT)
  RETURNS INT
BEGIN
  DECLARE earth_radius FLOAT;
  DECLARE d_lat FLOAT;
  DECLARE d_lng FLOAT;
  DECLARE a FLOAT;
  DECLARE c FLOAT;
  DECLARE dist FLOAT;

  SET earth_radius = 3958.75;

  SET d_lat = RADIANS(lat2 - lat1);
  SET d_lng = RADIANS(lng2 - lng1);

  SET a = sin(d_lat/2) * sin(d_lat/2) + cos(radians(lat1)) * cos(radians(lat2)) * sin(d_lng/2) * sin(d_lng/2);
  SET c = 2 * atan2(sqrt(a), sqrt(1-a));
  SET dist = earth_radius * c; 

  RETURN round((dist * 1609) / 1000);
END;
$$
DELIMITER ;