在EXP导出时，出现EXP-00091报错：
. . exporting table FRIEND
..............
142480 rows exported
EXP-00091: Exporting questionable statistics.
查看EXP-00091的oracle error message 解决方案说明：
[oracle@MWSG1: ~]$oerr exp 00091
00091, 00000, "Exporting questionable statistics."
// *Cause: Export was able export statistics, but the statistics may not be
// usuable. The statistics are questionable because one or more of
// the following happened during export: a row error occurred, client
// character set or NCHARSET does not match with the server, a query
// clause was specified on export, only certain partitions or
// subpartitions were exported, or a fatal error occurred while
// processing a table.
// *Action: To export non-questionable statistics, change the client character
// set or NCHARSET to match the server, export with no query clause,
// export complete tables. If desired, import parameters can be
// supplied so that only non-questionable statistics will be imported,
// and all questionable statistics will be recalculated.
在我们做exp的过程中可能经常会遇到EXP-00091: Exporting questionable statistics.这样的EXP信息，其实它就是exp的error message，它产生的原因是因为我们exp工具所在的环境变量中的NLS_LANG与DB中的NLS_CHARACTERSET不一致。
⑴ 我们来查看DB中的NLS_CHARACTERSET的值（提供两种方法）：
sys@CCDB> select * from nls_database_parameters t where t.parameter='NLS_CHARACTERSET';
PARAMETER VALUE
------------------------- ---------------
NLS_CHARACTERSET AL32UTF8
-- 或者
sys@CCDB> select * from v$nls_parameters where parameter='NLS_CHARACTERSET';
PARAMETER VALUE
------------------------- ---------------
NLS_CHARACTERSET AL32UTF8
⑵ 查看环境变量中的NLS_LANG：
[oracle@MWSG1: ~]$echo $NLS_LANG
AMERICAN_AMERICA.ZHS16CGB231280 -- 果然与DB中NLS_CHARACTERSET＝AL32UTF8不同。
⑶ 根据⑴查出的NLS_CHARACTERSET（AL32UTF8）来设定exp的环境变量：
WINNT> set NLS_LANG=AMERICAN_AMERICA.AL32UTF8
[oracle@MWSG1: ~]$export NLS_LANG=AMERICAN_AMERICA.AL32UTF8
[oracle@MWSG1: ~]$echo $NLS_LANG
AMERICAN_AMERICA.AL32UTF8 -- 设置与DB中NLS_CHARACTERSET＝AL32UTF8相同。
⑷ 再来EXP导出数据 查看log中是否还有EXP-00091报错？
. . exporting table FRIEND
...........................................................................
..............................................
1216253 rows exported
. . exporting table FRIEND_GRP
128 rows exported
Export terminated successfully without warnings. -- 成功导出且没警告。
EXP-00091问题解决了！
– The End –