oracle--分組后獲取每組數據第一條數據

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='就診中'
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  ;

　　參考：

[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，需要查第幾條數據或需要查詢指定條數的數據——where rn=N or where rn in(num1,num2,numx,......)