After running upgrade for Moodle 2.0 from 1.95, the following error occurs.

Debug info: Unknown column 'a.question' in 'on clause'

SELECT qa.*, q.qtype
FROM mdl_question_answers qa
JOIN mdl_question q ON a.question = q.id
[array (
)]
Stack trace:

• line 391 of /lib/dml/moodle_database.php: dml_read_exception thrown
• line 691 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
• line 5068 of /lib/db/upgrade.php: call to mysqli_native_moodle_database->get_recordset_sql()
• line 1309 of /lib/upgradelib.php: call to xmldb_main_upgrade()
• line 264 of /admin/index.php: call to upgrade_core()