對(duì)一個(gè)DBA或需使用exp,imp的普通用戶來(lái)說(shuō)，在我們做exp的過(guò)程中可能經(jīng)常會(huì)遇到EXP－00091 Exporting
questionable statistics.這樣的EXP信息，其實(shí)它就是exp的error
message，它產(chǎn)生的原因是因?yàn)槲覀僥xp工具所在的環(huán)境變量中的
NLS_LANG與DB中的
NLS_CHARACTERSET不
一致。但需說(shuō)明的是，exp-91這個(gè)error
message對(duì)所生成的dump檔沒(méi)有影響，生成的dump檔還可以正常的imp（個(gè)人體會(huì)，不知道有沒(méi)有錯(cuò)），雖然它對(duì)我們的dump檔沒(méi)有影響，我
個(gè)人還是不想它出現(xiàn)，大家也有同感吧， 。。下面我們就讓它消失吧。。我們一起來(lái)
step 01 查看DB中的NLS_CHARACTERSET的值（提供兩種方法）：
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
step 02 根據(jù)step 01查出的NLS_CHARACTERSET（ZHT16BIG5）來(lái)設(shè)定exp的環(huán)境變量：
WINNT> set NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5
LINUX> export NLS_LANG=AMERICAN_AMERICA.ZHT16BIG5
附上exp-91的oracle error message 解決方案說(shuō)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.
From: http://vongates.itpub.net/post/2553/18625