下面看一个试验 ,验证的是只导出数据后，可以恢复，就算是表结构已经变化了，他也能把相应的列恢复，
1)SQL> desc liuwenhe.liuwenhe;
?Name? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? Null?? ? Type
?----------------------------------------- -------- ----------------------------
?X? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? NOT NULL NUMBER(38)
?Y? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? NUMBER(38)
2)SQL> select * from liuwenhe.liuwenhe;
? ? ? ? X? ? ? ? ? Y
---------- ----------
Export: Release 11.2.0.3.0 - Production on Mon Jul 6 11:52:56 2015
Copyright (c) 1982, 2011, Oracle and/or its affiliates.? All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
Starting "SYSTEM"."SYS_EXPORT_TABLE_03":? system/******** directory=bak dumpfile=hhhf.dmp tables=liuwenhe.liuwenhe
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 64 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/INDEX/INDEX
Processing object type TABLE_EXPORT/TABLE/CONSTRAINT/CONSTRAINT
Processing object type TABLE_EXPORT/TABLE/INDEX/STATISTICS/INDEX_STATISTICS
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "LIUWENHE"."LIUWENHE"? ? ? ? ? ? ? ? ? ? ? 5.492 KB? ? ? 6 rows
Master table "SYSTEM"."SYS_EXPORT_TABLE_03" successfully loaded/unloaded
******************************************************************************
Dump file set for SYSTEM.SYS_EXPORT_TABLE_03 is:
? /backup/expdp/hhhf.dmp
Job "SYSTEM"."SYS_EXPORT_TABLE_03" successfully completed at 11:53:10
4)SQL> alter table liuwenhe.liuwenhe? drop column y;
?
Table altered.
5)SQL> truncate table liuwenhe.liuwenhe;
?
Table truncated.
6)[oracle@rac1 expdp]$ impdp system/manager123 directory=bak dumpfile=hhhf.dmp tables=liuwenhe.liuwenhe? content=data_only;
?
Import: Release 11.2.0.3.0 - Production on Mon Jul 6 11:55:07 2015
Copyright (c) 1982, 2011, Oracle and/or its affiliates.? All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Real Application Clusters, OLAP, Data Mining
and Real Application Testing options
Master table "SYSTEM"."SYS_IMPORT_TABLE_04" successfully loaded/unloaded
Starting "SYSTEM"."SYS_IMPORT_TABLE_04":? system/******** directory=bak dumpfile=hhhf.dmp tables=liuwenhe.liuwenhe content=data_only
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
. . imported "LIUWENHE"."LIUWENHE"? ? ? ? ? ? ? ? ? ? ? 5.492 KB? ? ? 6 rows
Job "SYSTEM"."SYS_IMPORT_TABLE_04" successfully completed at 11:55:13
7)SQL> select * from liuwenhe.liuwenhe;
? ? ? ? X
----------
? ? ? ? 1
? ? ? ? 2
? ? ? ? 3
? ? ? ? 4
? ? ? ? 5
? ? ? ? 6
6 rows selected.
总结：Oracle数据泵，逻辑备份和恢复工具，他直接在逻辑从面操作，不能想象成单纯的insert ， 而且只导出数据，然后恢复数据时候，可以不用写remap_tablespace这个参数 ，tables=liuwenhe.liuwenhe? 这里要是没有写前缀liuwenhe,而写成tables=liuwenhe,系统就认为是system用户下的liuwenhe表，而出错。