oracle top 替代方案
清泛原创
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。
select * from (
select * from xxx order by xx
) where rownum <= 100
等同于SQL：select top 100 * from xxx order by xx。 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。
select * from (
select * from xxx order by xx
) where rownum <= 100
等同于SQL：select top 100 * from xxx order by xx。