如何在字符串里取出数字

set global log_bin_trust_function_creators=1;
drop function if exists GetNum;
CREATE FUNCTION GetNum (Varstring varchar(50)) RETURNS varchar(30)
BEGIN
  DECLARE v_length INT DEFAULT 0;
  DECLARE v_Tmp varchar(50) default '';
  set v_length=CHAR_LENGTH(Varstring);
  WHILE v_length > 0 DO
 
    if (ASCII(mid(Varstring,v_length,1))>47 and ASCII(mid(Varstring,v_length,1))<58) then
 
        set v_Tmp=concat(v_Tmp,mid(Varstring,v_length,1));
    end if;
    SET v_length = v_length - 1;
  END WHILE;
    RETURN REVERSE(v_Tmp);
END;

select getnum('12倒萨3ppp3张三4覅5')