对一个DBA或需使用exp,imp的普通用户来说，在我们做exp的过程中可能经常会遇到EXP－00091 Exporting questionable statistics.这样的EXP信息，其实它就是exp的error message，它产生的原因是因为我们exp工具所在的环境变量中的NLS_LANG与DB中的NLS_CHARACTERSET不一致。但需说明的是，exp-91这个error message对所生成的dump档没有影响，生成的dump档还可以正常的imp（个人体会，不知道有没有错），虽然它对我们的dump档没有影响，我个人还是不想它出现，大家也有同感吧，　。。下面我们就让它消失吧。。我们一起来

step 01　查看DB中的NLS_CHARACTERSET的值（提供两种方法）：

select * from nls_database_parameters t where t.parameter='NLS_CHARACTERSET'

orselect * from v$nls_parameters where parameter='NLS_CHARACTERSET';SQL> select * from v$nls_parameters where parameter='NLS_CHARACTERSET';

PARAMETER　　　　 VALUE

-----------------------　　----------------------------------------------NLS_CHARACTERSET ZHT16BIG5

step 02　根据step 01查出的NLS_CHARACTERSET（ZHT16BIG5）来设定exp的环境变量：

WINNT> set NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5

LINUX> export NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5

附上exp-91的oracle error message 解决方案说明：

oerr exp 91

00091, 00000, "Exporting questionable statistics."// *Cause: Export was able export statistics, but the statistics may not be// usuable. 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.// *Action: To export non-questionable statistics, change the client character// set or NCHARSET to match the server, export with no query clause,// 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.

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