說明：
EXP-00091: 出口可疑的統計。
EXP-00091: Exporting questionable statistics.

產生：
在數據庫的服務器端和客戶端字符集不同的情況下，導出(dump)數據庫表時，會產生這個錯誤。
雖然產生這個錯誤，但好像對導入沒有影響。

解決：

服務器端數據的字符集查看方法：
1、打開SQLPLUS，用sys用戶登錄。
2、執行SELECT * FROM V$NLS_PARAMETERS WHERE PARAMETER='NLS_CHARACTERSET';。
?? 其中'NLS_CHARACTERSET'必須為大寫。

PARAMETER
--------------------
VALUE
--------------------
NLS_CHARACTERSET
ZHS16GBK

（Linux)
在oracle用戶的.bash_profile文件加入
export NLS_LANG=AMERICAN_AMERICA.ZHS16GBK

（Windows）
1、打開注冊表，依次進入HKEY_LOCAL_MACHINE→SOFTWARE→ORACLE→HOME0目錄。
2、察看NLS_LANG的值。
3、將其修改為數據庫服務器端字符集相同的字符。
或
臨時設定環境變量
set NLS_LANG=AMERICAN_AMERICA.ZHS16GBK

附上exp-91的oracle error message 解決方案說明：

?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.

?