mysql查询所有子结点

select portal_company_org_id from (
              select t1.portal_company_org_id,
              if(find_in_set(parent_id, @pids) > 0, @pids := concat(@pids, ',', portal_company_org_id), 0) as ischild
              from (
                   select portal_company_org_id,parent_id from portal_company_org t order by parent_id, portal_company_org_id
                  ) t1,
                  (select @pids := 6024(要查询的结点) id) t2
             ) t3 where ischild != 0