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
---------- ----------
1
3
3
3
2
4
4
5
5
8
6
9
6 rows selected.
3)[Oracle@rac1 expdp]$ expdp system/manager123 directory=bak dumpfile=hhhf.dmp tables=liuwenhe.liuwenhe;
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。
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