Oracle 子查询，按降序排列，取前n条

比如，有一个student 表：

 

id             student_name     

1                                  s1

2                                  s2

03                                s3

04                                s4

05                                s5

06                                s6

07                                s7

08                                s8

09                                s9

 

这些id 不一致，比如我想把id 变成 1， 2， 3（而不用03），4， 5 ， 6, 7， 8， 9

 

可执行如下操作：

update  student a set a.id =(select substr(b.id,-1) from student b where b.id=a.id)
where a.id >2;

commit;

之后结果变为：

 

id             student_name     

1                                  s1

2                                  s2

3                                s3

4                                s4

5                                s5

6                                s6

7                                s7

8                                s8

9                                s9

 

之后，想通过子查询的方式，按倒序显示前6条记录：

 

select * from (select * from student order by id desc)
where rownum <= 6;

 

结果为：

 

id             student_name     

9                    s9

8                    s8

7                    s7

6                    s6

5                    s5

4                    s4