I am with 2.0.1.
When I check the quiz -> Results -> Grade, on the top of the page, there are 2 options, if I select "that are graded for each user (Highest grade), (please see the attachment), then I get the following Oracle database error message:
Default exception handler: Error reading from database Debug: ORA-01799: a column may not be outer-joined to a subquery\nSELECT qqr.* FROM m_user u LEFT JOIN m_quiz_attempts qa ON qa.userid = u.id AND qa.quiz = :quizid AND qa.sumgrades = (SELECT MAX(qa2.sumgrades) FROM m_quiz_attempts qa2 WHERE qa2.quiz = qa.quiz AND qa2.userid = qa.userid) AND qa.timestart = (SELECT MIN(qa3.timestart) FROM m_quiz_attempts qa3 WHERE qa3.quiz = qa.quiz AND qa3.userid = qa.userid AND qa3.sumgrades = qa.sumgrades), m_quiz_question_regrade qqr WHERE qqr.attemptid = qa.uniqueid AND u.id IN (:u0000,:u0001,:u0002) AND qa.id IS NULL\n[array (\n 'quizid' => '5',\n 'u0000' => 283,\n 'u0001' => 284,\n 'u0002' => 217,\n 'oracle_num_rows' => 1,\n)]\n* line 391 of /lib/dml/moodle_database.php: dml_read_exception thrown\n* line 268 of /lib/dml/oci_native_moodle_database.php: call to moodle_database->query_end()\n* line 1043 of /lib/dml/oci_native_moodle_database.php: call to oci_native_moodle_database->query_end()\n* line 110 of /mod/quiz/report/reportlib.php: call to oci_native_moodle_database->get_records_sql()\n* line 258 of /mod/quiz/report/overview/report.php: call to quiz_get_regraded_qs()\n* line 90 of /mod/quiz/report.php: call to quiz_overview_report->display()\n, referer: http://our.tests.erver.edu/mod/quiz/report.php