之前发表过一篇关于IMP/EXP的文章，有兴趣可以先了解下：EXP/IMP数据迁移
exp：根据谓词短语，导出表中的一部分数据，可以指定分区：
[lubinsu@localhost orcl]$ exp lubinsu/lubinsu file=serv_msg.dmp tables=serv_msg:p_nj query=" where latn_id = 250 " log=serv_msg.log compress=y
Export: Release 10.2.0.1.0 - Production on Wed Jun 26 22:46:02 2013
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
Export done in ZHS16GBK character set and AL16UTF16 NCHAR character set
About to export specified tables via Conventional Path ...
. . exporting table SERV_MSG
. . exporting partition P_NJ 10008 rows exported
EXP-00091: Exporting questionable statistics.
Export terminated successfully with warnings.
[lubinsu@localhost orcl]$ ll
total 2536
-rw-rw-r-- 1 lubinsu lubinsu 2580480 Jun 26 22:46 serv_msg.dmp
-rw-rw-r-- 1 lubinsu lubinsu 493 Jun 26 22:46 serv_msg.log
以上导出的同时会导出相关的统计信息。
但是在导出过程中可能会提示：
EXP-00091 Exporting questionable statistics
因为如果在导出时，添加了谓词短语，则可能导致统计信息对于导出的数据并不准确，所以提示导出的统计信息不可用，这是合理的
如果不想看到这些统计信息，则可以，添加statistics=none，则不会导出相关的统计信息：
[lubinsu@localhost orcl]$ exp lubinsu/lubinsu file=serv_msg.dmp tables=serv_msg:p_nj query=" where latn_id = 250 " log=serv_msg.log compress=y statistics=none
Export: Release 10.2.0.1.0 - Production on Wed Jun 26 22:47:54 2013
Copyright (c) 1982, 2005, Oracle. All rights reserved.
Connected to: Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options
Export done in ZHS16GBK character set and AL16UTF16 NCHAR character set
About to export specified tables via Conventional Path ...
. . exporting table SERV_MSG
. . exporting partition P_NJ 10008 rows exported
Export terminated successfully without warnings.
官方文档是这么说的：
The Oracle docs note this on the EXP-00091 error:
EXP-00091 Exporting questionable statistics
--原因
Cause: Export was able to export statistics, but the statistics may not be useable. The statistics are questionable because one or more of the following happened during export:
- A row error occurred, client character set or NCHARSET does not match with the server, a query clause was specified on export,
- Only certain partitions or subpartitions were exported, or a fatal error occurred while processing a table.
--解决方法
Action: To export non-questionable statistics, change the client character set or NCHARSET to match the server, export with no query clause, or export complete tables.
If desired, import parameters can be supplied so that only non-questionable statistics will be imported, and all questionable statistics will be recalculated.