create function getParentList(rootId varchar(100)) returns varchar(1000)
BEGIN   
DECLARE fid varchar(100) default '';   
DECLARE str varchar(1000) default rootId;   
  
WHILE rootId is not null  do   
    SET fid =(SELECT relativeserialno FROM flow_task WHERE serialno = rootId);   
    IF fid is not null THEN   
        SET str = concat(str, ',', fid);   
        SET rootId = fid;   
    ELSE   
        SET rootId = fid;   
    END IF;   
END WHILE;   
return str;  
END;