Distance calculator

f_distance.sql

-- http://www.sqlexamples.info/SPAT/mysql_distance.htm
DROP FUNCTION IF EXISTS fn_distance;
DELIMITER $$
CREATE FUNCTION fn_distance(
	p_x1 FLOAT, p_y1 FLOAT, 
	p_x2 FLOAT, p_y2 FLOAT
)
RETURNS FLOAT
DETERMINISTIC
BEGIN
	DECLARE v_dist FLOAT;
	DECLARE A FLOAT; DECLARE B FLOAT;
	DECLARE C FLOAT; DECLARE D FLOAT;

	/**
	* Returns distance calculation between two points in LAT-LONG coordinates
	*/
	SET v_dist = 0;

	-- Convert to radians
	SET A = p_x1 / 57.29577951;
	SET B = p_y1 / 57.29577951;
	SET C = p_x2 / 57.29577951;
	SET D = p_y2 / 57.29577951;

	IF (A = C && B = D) THEN
		SET v_dist = 0;
	ELSEIF ((SIN(A)*SIN(C)+COS(A)*COS(C)*COS(B - D)) > 1) THEN
		SET v_dist = 3963.1 * ACOS(1); 
	ELSE 
		SET v_dist = 3963.1*ACOS(SIN(A)*SIN(C) + COS(A)*COS(C)*COS(B - D));
	END IF;

	/* Return distance in km. */ 
	SET v_dist = v_dist * 1.609;
	RETURN v_dist;
END $$

/* Distance from Duomo to Castello Sforzesco */ 
SELECT fn_distance (9.1918377,45.4642822,9.1794726,45.4702864) AS dist_km;