Tableau has identified a deviation in the ODBC standard specific to Oracle's ability to perform random or percentage data retrieval in the Tableau data extraction dialogue. Because of this deficiency, you may see the "Database error 0x80004005: [Oracle][ODBC][Ora]ORA-00936: missing expression, Unable to create extract" error message when you are connecting to an Oracle data source using the generic ODBC connection in Tableau and then attempting to perform a Tableau extraction by choosing a random percentage or row count.
The recommended solution is to use the native Oracle drivers instead of ODBC. Tableau Software supports direct connections to Oracle using the oci.dll driver set, which is available from the Drivers page. There should be no reason to use an ODBC connection when connecting to Oracle data sources.