Teachers can't view the summary of the quizzes answered by their students. It's a specific problem related with Oracle. To solve it it's necessary to edit the mod/quiz/report/overview/report.php file, go to the quiz_report/display method and remove the "AS" in the SQL query in the following line (line 410 aprox.):

ORIGINAL:
$from .= " JOIN {$CFG->prefix}quiz_feedback AS qf ON " .

NEW (it works OK for Oracle and for MySQL):
$from .= " JOIN {$CFG->prefix}quiz_feedback qf ON " .

We attach also the file agora_quiz_problem.png to show you what was happening before to solve the problem.