sql高手帮忙

SQL code:
select i.card_id,
(select m.names from
(select rownum as r ,t.code_detail,d.names from infectiondetail t, infection_steps d where t.code_detail = d.code and t.infection_cardid = i.card_id order by t.dt_start desc,t.addtime desc) m
where m.r<2
) diseaasestageName
from infectioncard i
where i.card_id ='-59052'



结果：card_id diseaasestageName
  -59052 死亡期


SQL code:

select i.card_id,
(select m.names from
(select rownum as r ,t.code_detail,d.names from infectiondetail t, infection_steps d where t.code_detail = d.code and t.infection_cardid = '-59052' order by t.dt_start desc,t.addtime desc) m
where m.r<2
) diseaasestageName
from infectioncard i
where i.card_id ='-59052'


结果：card_id diseaasestageName

  -59052  

为什么前一个 的diseaasestagename有值，后一个就没值呢？？

---

rownum是一个伪列，如果有排序，它是先分配rownum，再order by，所以要想先order by，后rownum，请用子查询先order by操作
SQL code:
SELECT i.card_id,
(SELECT rownum, m.names
from