oracle分组取每组第一条数据，oracle每组

oracle分组取每组第一条数据，oracle每组

oracle分组后取每组第一条数据   ‘数据格式     分组取第一条的效果    

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

oracle进行分组后，取出每组的前几条数据SELECT *FROM (SELECT 分组的字段名,ROW_NUMBER() OVER(PARTITION BY 分组的字段名 ORDER BY 排序的字段名) AS RNFROM 表名)WHERE RN <= 10??
 

select * from 表名 a where exists (select top 2 * from
(select a,a1,a2 from 表名 group by a,a2) b where a.a=b.a and a.a2=b.a2)