Use sql_in_set as designed and consistent with the rest of phpBB code in phpbb_notification_manager

		$sql = 'UPDATE ' . $this->notifications_table . "

			SET notification_read = 1

			WHERE item_type = '" . $this->db->sql_escape($item_type) . "'

				AND notification_time <= " . (int) $time .

				(($item_parent_id !== false) ? ' AND ' . (is_array($item_parent_id) ? $this->db->sql_in_set('item_parent_id', $item_parent_id) : 'item_parent_id = ' . (int) $item_parent_id) : '') .

				(($user_id !== false) ? ' AND ' . (is_array($user_id) ? $this->db->sql_in_set('user_id', $user_id) : 'user_id = ' . (int) $user_id) : '');

		$this->db->sql_query($sql);