非常感谢@caozhy 帮助，根据你提供的链接，已经搞定，3Q;
下面为我写出的方法，供大家参阅；水平有限，勿喷。

-- 取字符串中的多个数值（只可以是整型数值），获取最大值
CREATE DEFINER=root@localhost FUNCTION FindMaxNumber(_input VARCHAR(64)) RETURNS INTEGER
BEGIN
DECLARE _r VARCHAR(32) DEFAULT '';
DECLARE _i INTEGER DEFAULT 1;
DECLARE _t BOOLEAN DEFAULT TRUE;
DECLARE _start INTEGER DEFAULT 0;
DECLARE _IsCharNumeric BOOLEAN;
DECLARE _maxnum INTEGER DEFAULT 0;
DECLARE _num INTEGER DEFAULT 0;

WHILE _i < length(_input) DO
_loop: REPEAT
SET _IsCharNumeric = locate(mid(_input, _i, 1), "0123456789") > 0;
IF _IsCharNumeric THEN
IF _t THEN
SET _t = FALSE;
SET _start = _i;

END IF;
ELSE
IF _start > 0 THEN LEAVE _loop; END IF;
END IF;
SET _i = _i + 1;
UNTIL _i > length(_input) END REPEAT;

  IF _start > 0 AND NOT _t THEN
    SET _t = TRUE;
    SET _r = mid(_input, _start, _i - _start);
    SET _num = convert(_r,SIGNED);
    SET _maxnum = greatest(_maxnum,_num);
  END IF;
  SET _i = _i+1; 

END WHILE;
RETURN _maxnum;
END