Using the same parameter more than once in an SQL query causes an exception

        if ($count > count($params)) {

            $a = new stdClass;

            $a->expected = $count;

            $a->actual = count($params);

            throw new dml_exception('invalidqueryparam', $a);

        }

        list($usql, $params) = $DB->get_in_or_equal($this->mainobject->students->ids->$courseid,

                                                    SQL_PARAMS_NAMED, 'param0000');

        list($usql2, $params2) = $DB->get_in_or_equal($this->mainobject->teachers,

                                                      SQL_PARAMS_NAMED, 'param900000', false);

        $sql = "SELECT p.id as post_id, p.userid, d.firstpost, f.course, f.type, f.id, f.name,

                       f.intro as description, c.id as cmid

                  FROM {forum} f

            INNER JOIN {course_modules} c

                    ON f.id = c.instance

            INNER JOIN {forum_discussions} d

                    ON d.forum = f.id

            INNER JOIN {forum_posts} p

                    ON p.discussion = d.id

             LEFT JOIN {forum_ratings} r

                    ON p.id = r.post

                 WHERE p.userid <> :userid

                   AND p.userid $usql

                   AND (((r.userid <> :userid) AND (r.userid $usql2))

                       OR r.userid IS NULL)

                   AND ((f.type <> 'eachuser') OR (f.type = 'eachuser' AND p.id = d.firstpost))

                   AND c.module = :moduleid

                   AND c.visible = 1

                   AND f.course = :courseid

                   AND f.assessed > 0

              ORDER BY f.id";

        $params = array_merge($params, $params2);

        $params['userid'] = $USER->id;

        $params['moduleid'] = $this->mainobject->modulesettings['forum']->id;

        $params['courseid'] = $courseid;

        $unmarked = $DB->get_records_sql($sql, $params);

        $count = 0;

        if ($named_count) {

            $type = SQL_PARAMS_NAMED;

            $removedduplicates = array_unique($named_matches);

            $count = count($removedduplicates);

        }