While testing PULL-423 (see http://tracker.moodle.org/browse/PULL-423?focusedCommentId=106553&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-106553), oracle/mod/quiz/report.php errored with:

Debug info: ORA-00918: column ambiguously defined
SELECT u.id || '#' || COALESCE(qa.attempt, 0) AS concattedid, (CASE WHEN 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) THEN 1 ELSE 0 END) AS gradedattempt, qa.uniqueid,
qa.id AS attempt,
u.id AS userid,
u.idnumber,
u.firstname,
u.lastname,
u.picture,
u.imagealt,
u.email,
u.institution,
u.department,
qa.sumgrades,
qa.timefinish,
qa.timestart,
qa.timefinish - qa.timestart AS duration,
CASE WHEN qa.timefinish = 0 THEN null
WHEN qa.timefinish > qa.timestart THEN qa.timefinish - qa.timestart
ELSE 0 END AS duration FROM m_user u LEFT JOIN m_quiz_attempts qa ON qa.userid = u.id AND qa.quiz = :quizid WHERE qa.id IS NOT NULL AND qa.preview = 0 ORDER BY concattedid ASC
[array (
'quizid' => '21',
'oracle_num_rows' => 30,
)]
Stack trace:
line 391 of \lib\dml\moodle_database.php: dml_read_exception thrown
line 268 of \lib\dml\oci_native_moodle_database.php: call to moodle_database->query_end()
line 1042 of \lib\dml\oci_native_moodle_database.php: call to oci_native_moodle_database->query_end()
line 1354 of \lib\tablelib.php: call to oci_native_moodle_database->get_records_sql()
line 244 of \mod\quiz\report\responses\responses_table.php: call to table_sql->query_db()
line 1375 of \lib\tablelib.php: call to quiz_report_responses_table->query_db()
line 348 of \mod\quiz\report\responses\report.php: call to table_sql->out()
line 90 of \mod\quiz\report.php: call to quiz_responses_report->display()