[oracle] rownum、order by 组合实现top N

在Oracle中实现select top N: 由于Oracle不支持select top 语句，所以在Oracle中经常是用order by 跟rownum 的组合来实现select top n的查询。 简单地说，实现方法如下所示：

select 列名1 ...列名n from ( select 列名1 ...列名n    from 表名 order by 列名1 ) where rownum <=N(抽出记录数) order by rownum asc

如：select id,name from (select id,name from student order by name) where rownum<=10 order by rownum asc

按姓名排序取出前十条数据

附：取100-150条数据的方法

1. 最佳选择：利用分析函数

       row_number() over ( partition by col1 order by col2 )                               

比如想取出100-150条记录,按照tname排序      select tname,tabtype from (                               

     select tname,tabtype,row_number() over ( order by tname ) rn from tab                

) where rn between 100 and 150;

2. 使用rownum 虚列

select tname,tabtype from (                    

      select tname,tabtype,rownum rn from tab where rownum <= 150                  

) where rn >= 100;

文章来源:http://www.cnblogs.com/yangxia-test/archive/2012/09/20/2695617.html