When trying to do a Oracle database dump or export, be it full entire database export or a particular user or table export, the following message may appears right after status of exporting a table.

EXP-00091: Exporting questionable statistics.

The cause for this error is because statistics may not be useable although Export was able to export statistics. The statistics are questionable because one or more of the following happened during export:

  • A row error occurred
  • Client character set or NCHARSET (where you run the Export) does not match with the server (database character set)
  • A query clause was specified on export, only certain partitions or subpartitions were exported
  • A fatal error occurred while processing a table

The resolution is to export non-questionable statistics, change the client character set or NCHARSET to match the server, export with no query clause, or export complete tables.

Most commonly, the EXP-00091 happens when the character set of client where Exp is running is different from character set of Oracle database server.

To solve this issue, try setting the NLS_LANG environment variable at the OS level, prior to the export session, to match your database character set. Syntax as follow, change the character set to your database’s character set.

export NLS_LANG=WE8ISO8859P1

For easier way of resolution, export with option “STATISTICS=NONE”. Also, if you’re using Oracle 10g, use Oracle Date Pump’s expdp and impdp instead of instead of exp and imp to export and import the data.

It’s pretty safe to say that if EXP-00091 is the only error message, the export’s row data is without any problems. If desired, import parameters can be supplied so that only non-questionable statistics will be imported, and all questionable statistics will be recalculated.

At the beginning of Export, the charset of the database will be shown. Else, you will need to use “show parameter nls” in SQL*Plus to check what charset the Oracle database is using.