两种分页排序比较

1. 

select a.*
  from (select t.*, rownum rownum_
          from (select * from project c order by c.project_name) t
         where rownum <= 20) a
 where rownum_ >= 1;

由执行计划可知，其先进行全表扫描，而后再进行全表排序，只会再取分页子集

2. 

SELECT *
  FROM (SELECT ROWNUM AS rowno, c.*
          FROM project c
         WHERE ROWNUM <= 20
         order by c.project_name) table_alias
 WHERE table_alias.rowno >= 1;

虽然2的效率可能不如1，但1也许不是我们所想要的排序方式。