Algorithm of Haversine to calculate distance between two gps coord for MySQL

haversine.sql

  DELIMITER //
  CREATE FUNCTION `distance` (p1_latitude DOUBLE, p1_longitude DOUBLE, p2_latitude DOUBLE, p2_longitude DOUBLE) RETURNS DOUBLE
  BEGIN
      DECLARE deg2rad DOUBLE DEFAULT 0.0174; -- 3.14/180 or 2PI/360
      DECLARE distance_latitude, distance_longitude, a DOUBLE;  
      SET distance_latitude = ( p2_latitude  - p1_latitude  ) * deg2rad;
      SET distance_longitude = ( p2_longitude - p1_longitude ) * deg2rad;
      SET a = sin( distance_latitude * .5 ) * sin( distance_latitude * .5 ) + cos( p1_latitude * deg2rad ) * cos( p2_latitude * deg2rad ) * sin( distance_longitude / 2 ) * sin( distance_longitude / 2 );
      RETURN round( ( 2 * atan2( sqrt(a) , sqrt(1-a) ) ) * 6371000 , 3 ); -- 6371000 : curve rayon of earth ;
  END
  //
  DELIMITER ;