oracle--分组后获取每组数据第一条数据

SELECT *
   FROM (SELECT ROW_NUMBER() OVER(PARTITION BY cc.queuename ORDER BY cc.enroldate DESC) rn,
         cc.*
         FROM
         (select * from
(select a.patname,a.queuesign,a.queuename,a.status,a.checkroom,a.areapart,a.enroldate
from qs_register a where a.status='就诊中'
group by a.patname,a.queuesign,a.queuename,a.status,a.checkroom,a.areapart,a.enroldate
order by a.queuename,a.status,a.enroldate) bb)cc
         )
  WHERE rn = 1  ;

　　参考：

[sql]
SELECT *
   FROM (SELECT ROW_NUMBER() OVER(PARTITION BY x ORDER BY y DESC) rn,
         test1.*
         FROM test1)
  WHERE rn = 1  ;

　　注：同理而言，需要查第几条数据或需要查询指定条数的数据——where rn=N or where rn in(num1,num2,numx,......)