问题描述：
使用oracle用户进行导出时，报以下错误:
Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
Export done in US7ASCII character set and AL16UTF16 NCHAR character set
server uses ZHS16GBK character set (possible charset conversion)

About to export specified users ...
. exporting pre-schema procedural objects and actions
. exporting foreign function library names for user PLATFORM
. exporting PUBLIC type synonyms
. exporting private type synonyms
. exporting object type definitions for user PLATFORM
About to export PLATFORM's objects ...
. exporting database links
. exporting sequence numbers
. exporting cluster definitions
. about to export PLATFORM's tables via Conventional Path ...
. . exporting table               CL_WORD_TEMPLATE          0 rows exported
EXP-00091: Exporting questionable statistics.
. . exporting table                     PLAN_TABLE          0 rows exported
EXP-00091: Exporting questionable statistics.
. . exporting table                       S_ACTION        242 rows exported
1.查看错误原因和解决办法
[oracle@localhost backup]$ 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.
服务器端字符集和客户端字符集不一致
2.查看数据库字符集

SQL> select * from nls_database_parameters where parameter like '%CHARACTERSET%';

PARAMETER                                                    VALUE
------------------------------------------------------------ --------------------
NLS_NCHAR_CHARACTERSET                                       AL16UTF16                     --国家字符集
NLS_CHARACTERSET                                             ZHS16GBK                            --数据库字符集
3.在oracle用户的.bash_profile中加入
export NLS_LANG=american_america.zhs16gbk
echo $NLS_LANG查看是否正确