http://mysql.rjweb.org/doc.php/find_nearest_in_mysql#gcdistdeg

ST_Distance_Sphere.sql

DELIMITER //
CREATE  FUNCTION `GCDistDeg`(
        _lat1 DOUBLE,
        _lon1 DOUBLE,
        _lat2 DOUBLE,
        _lon2 DOUBLE
    ) RETURNS double
    DETERMINISTIC
    SQL SECURITY INVOKER
    COMMENT 'Degrees in, Degrees out.  For conversion: 69.172 mi/deg or 111.325 km/deg'
BEGIN

    DECLARE _deg2rad DOUBLE DEFAULT PI()/180;
    DECLARE _rlat1 DOUBLE DEFAULT _deg2rad * _lat1;
    DECLARE _rlat2 DOUBLE DEFAULT _deg2rad * _lat2;

    DECLARE _rlond DOUBLE DEFAULT _deg2rad * (_lon1 - _lon2);
    DECLARE _m     DOUBLE DEFAULT COS(_rlat2);
    DECLARE _x     DOUBLE DEFAULT COS(_rlat1) - _m * COS(_rlond);
    DECLARE _y     DOUBLE DEFAULT               _m * SIN(_rlond);
    DECLARE _z     DOUBLE DEFAULT SIN(_rlat1) - SIN(_rlat2);
    DECLARE _n     DOUBLE DEFAULT SQRT(
                        _x * _x +
                        _y * _y +
                        _z * _z    );
    RETURN  2 * ASIN(_n / 2) / _deg2rad;
END
//