prerequisite:被删除的表空间创建时开始，数据库一直在archivelog模式下

恢复具体操作如下：
SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            F:\oracle\ora92\RDBMS
Oldest online log sequence     23
Next log sequence to archive   25
Current log sequence           25

SQL> alter tablespace backuptest offline;
alter tablespace backuptest offline
*
ERROR at line 1:
ORA-01109: database not open

SQL> alter database datafile 'f:\backup.dbf' offline;

Database altered.

SQL> alter database open;

Database altered.

SQL> alter tablespace backuptest offline immediate;

Tablespace altered.

SQL> select * from v$recover_file;

     FILE# ONLINE  ONLINE_ ERROR                                                                CHANGE# TIME
---------- ------- ------- ----------------------------------------------------------------- ---------- ---------
        11 OFFLINE OFFLINE FILE NOT FOUND                                                             0

SQL> alter database create datafile 'f:\backup.dbf' as 'f:\backup.dbf';

Database altered.

SQL> select * from v$recover_file;

     FILE# ONLINE  ONLINE_ ERROR                                                                CHANGE# TIME
---------- ------- ------- ----------------------------------------------------------------- ---------- ---------
        11 OFFLINE OFFLINE                                                                      3074706 03-NOV-04

SQL> recover tablespace backuptest;
Media recovery complete.
SQL> alter tablespace backuptest online;

Tablespace altered.

SQL> select * from backup;

        ID
----------
         1
         2

至此，已经完全恢复了^_^