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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