EXP-00091 Exporting questionable statistics

在我们对Oracle做EXP的过程中，可能会经常遇到EXP－00091 Exporting questionable statistics.的信息，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是的NLS LANG中的NLS_CHARCATERSET不一致引起的。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$nls_parameters  where parameter='NLS_CHARACTERSET';
SQL> select * from v$nls_parameters where parameter='NLS_CHARACTERSET';

PARAMETER　　　　      VALUE
-----------------------　　----------------------------------------------
NLS_CHARACTERSET    ZHT16BIG5

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

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中修改。
LINUX> export NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5

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.