Oracle 中的Top写法

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;