You have lost datafiles 1 and 3 from your database, and the database has crashed. In what order
should you perform the following steps to recover your database?
1. Take the datafiles that were lost offline.
2. startup mount the database
3. Issue the alter database open command.
4. Restore the datafiles that were lost
5. Recover the datafiles with the recover datafile command.
6. Bring the datafiles back online.
7. Recover the database with the recover database command.
A. 2, 1, 3, 4, 5, 6
B. 2, 4, 5, 3
C. 4, 7, 3
D. 2, 4, 7, 3
E. 2, 7, 3
注:解释说无法在线修复因为Datafile 1 一直是system的表空间，而数据库不能opened当system空间无效时。
开启挂载数据库→还原(restore)datafile→使用command恢复(recover)datafile→最后打开数据库
oracle中restore是还原恢复物理文件，recover是逻辑恢复，恢复数据。
You will have to startup mount the database and then restore the database datafiles
that were lost(you could,of course,restore the files first).You then need to recover the
datafiles with the recover datafile command.Once the datafiles are recovered,you can then
open the database.You may wonder why online recovery is not possible in this case.Datafile 1
always the SYSTEM tablespace.The database cannot be opened if the SYSTEM tablespace is
not available.Also the use of the recoveer databaser command is not the best choice.In this case
datafile recovery is the better choice.