EXP-00091 Exporting questionable statistics
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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.
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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.

解決：
linux下的oracle用戶的環境變量語言集和oralce數據庫中的環境變量語言集不相同。
查看oracle的環境變量語言集：
數據庫服務器字符集：
select * from nls_database_parameters
客戶端字符集：
select * from nls_instance_parameters

將oracle用戶的環境變量語言集改成和數據庫服務器字符集一樣。
?export NLS_LANG=american_america.ZHS16GBK