public function getChangelogMinDate()
    {
        $result = null;
        $asChange = 'c';
        $tblChange = $this->resource->getTableName(EChange::ENTITY_NAME);
        /* select from account */
        $query = $this->conn->select();
        $query->from([$asChange => $tblChange], [EChange::A_DATE_CHANGED]);
        /* order by */
        $query->order([$asChange . '.' . EChange::A_DATE_CHANGED . ' ASC']);
        /* perform query */
        $result = $this->conn->fetchOne($query);
        if ($result < self::DATE_MIN) {
            $result = self::DATE_MIN;
        }
        return $result;
    }