exp报错：EXP-00091 Exporting questionable statistics

对DBA或需使用exp,imp的普通用戶來说，在我们做exp的過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。但需要说明的是，EXP-00091这个error对所生成的dump文件没有影响，生成的dump文件还可以正常imp。

下面我们来解决这个问题，让其不再出现：

第一步：　

查看DB中的NLS_CHARACTERSET的值（提供两种方法）：

查询NLS_CHARACTERSET的值：
select * from nls_database_parameters t where t.parameter='NLS_CHARACTERSET'
or
select * from v$nls_parameterswhere parameter='NLS_CHARACTERSET';

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

PARAMETER　　　　VALUE
-----------------------　　----------------------------------------------
NLS_CHARACTERSETZHT16BIG5

第二步：　

根据第一步查出的NLS_CHARACTERSET（ZHT16BIG5）来设定exp的环境变量：

WINNT> set NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5  --windows环境

进行设定后，在环境变量中查看NLS_LANG的值是否一致，如果不一致可在环境变量中手动修改。

LINUX> export NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5  --linux环境
LINUX> exp 导出语句

附上exp-00091的oracle error message 解決方案说明：

error 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.