mysql 查询所有下级

select *,ischild from (
	select t1.*,
	if(find_in_set(u_parent_id, @pids) > 0, @pids := concat(@pids, ',', u_id), 0) as ischild
	from (
			 select * from tb_user t order by u_parent_id, u_id
			) t1,
			(select @pids := 某个节点的id) t2
 ) t3 where ischild != 0

说明：只需关注u_parent_id,u_id,字段和tb_user表，将这些替换成自己的表和字段即可，其他查询条件可最后拼接