CREATE TABLE `demo` (
 `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
 `tid` int(11) DEFAULT '0',
 `pid` int(11) DEFAULT '1',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3000124 DEFAULT CHARSET=utf8;

CREATE DEFINER=`root`@`localhost` FUNCTION `lvtao_demo_a`(rootId int) RETURNS text CHARSET utf8
  READS SQL DATA
  COMMENT 'demo'
BEGIN

DECLARE sTemp text;
DECLARE sTempChd text;

SET sTempChd =cast(rootId as CHAR);
SET sTemp = '';

WHILE sTempChd is not null DO
  SET sTemp = concat(sTemp,',',sTempChd);
  SELECT group_concat(id) INTO sTempChd FROM demo where FIND_IN_SET(tid,sTempChd)>0;
END WHILE;

RETURN sTemp;

END;

select lvtao_demo_a(5);

Data too long for column 'sTemp' at row 1

DELIMITER ;;
CREATE DEFINER=`root`@`localhost` PROCEDURE `sss`(IN pid int, IN rootid int)
BEGIN
   
DECLARE done INT DEFAULT FALSE;
DECLARE id TEXT;
DECLARE cur1 CURSOR FOR SELECT id FROM demo WHERE tid=pid;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

set max_sp_recursion_depth = 200;
 
OPEN cur1;
  read_loop: LOOP
    FETCH cur1 INTO id;
    IF done THEN
      LEAVE read_loop;
    END IF;
    INSERT INTO temp (rootid,zid) values (rootid, id);
    call sss(id,rootid);
  END LOOP;
CLOSE cur1;

END;;
DELIMITER ;