比如，有一個student 表：

id             student_name     

1                                  s1

2                                  s2

03                                s3

04                                s4

05                                s5

06                                s6

07                                s7

08                                s8

09                                s9

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

可執行如下操作：

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

commit;

之後結果變為：

id             student_name     

1                                  s1

2                                  s2

3                                s3

4                                s4

5                                s5

6                                s6

7                                s7

8                                s8

9                                s9

之後，想通過子查詢的方式，按倒序顯示前6條記錄：

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

結果為：

id             student_name     

9                    s9

8                    s8

7                    s7

6                    s6

5                    s5

4                    s4