表如上：

DELIMITER //
CREATE FUNCTION `getChildLst`(rootId INT)

RETURNS varchar(1000) READS SQL DATA

BEGIN
  DECLARE sTemp VARCHAR(1000);
  
  DECLARE sTempChd VARCHAR(1000);

  SET sTemp = '$';

  SET sTempChd =cast(rootId as CHAR);

  WHILE sTempChd is not null DO

    SET sTemp = concat(sTemp,',',sTempChd);
    
    SELECT group_concat(id) INTO sTempChd FROM t_files where FIND_IN_SET(parent_id,sTempChd)>0;

  END WHILE;

  RETURN sTemp;

END  //
DELIMITER ;

调动语句：

select *from t_files where find_in_set(id, getChildLst(1));