SQL>select file#,name,checkpoint_change# from v$datafile;

FILE#  NAME   CHECKPOINT_CHANGE#

......

13 F:\ORACLE\ORADATA\TEST\RMAN.DBF27259134244

14 F:\ORACLE\ORADATA\TEST\MAGGIE_DATA1.DBF27207207995

15 F:\ORACLE\ORADATA\TEST\BLOCK01.DBF 27259134244

SQL>select dbms_flashback.get_system_change_number from dual;

GET_SYSTEM_CHANGE_NUMBER

------------------------

27259186119

SQL>alter database datafile 15 offline;

数据库已更改

SQL>select file#,name,checkpoint_change# from v$datafile;

FILE#  NAME   CHECKPOINT_CHANGE#

......

13 F:\ORACLE\ORADATA\TEST\RMAN.DBF27259134244

14 F:\ORACLE\ORADATA\TEST\MAGGIE_DATA1.DBF27207207995

15 F:\ORACLE\ORADATA\TEST\BLOCK01.DBF 27259134244

SQL>select dbms_flashback.get_system_change_number from dual;

GET_SYSTEM_CHANGE_NUMBER

------------------------

27259186180

SQL>alter database datafile 15 online;

ORA-01113:文件15需要介质恢复

ORA-01110:数据文件15: 'F:\ORACLE\ORADATA\TEST\BLOCK01.DBF'

SQL>recover datafile 15;

完成介质恢复

SQL>alter database datafile 15 online;

数据库已更改

SQL>select file#,name,checkpoint_change# from v$datafile;

FILE#  NAME   CHECKPOINT_CHANGE#

......

13 F:\ORACLE\ORADATA\TEST\RMAN.DBF27259134244

14 F:\ORACLE\ORADATA\TEST\MAGGIE_DATA1.DBF27207207995

15 F:\ORACLE\ORADATA\TEST\BLOCK01.DBF 27259186244

ALTER DATABASE DATAFILE OFFLINE的时候不对datafile做checkpoint，offline后Checkpoint scn和stop scn是不一致的。stop scn比Checkpoint scn要大一点。所以online的时候要recover。

recover的过程是作了必要的前滚和回滚，并且使Checkpoint scn和stop scn一致，都变为offline后的stop scn的大小。

online以后又作了一次checkpoint，并且stop scn变为无穷大。