custom query in custructure in prestashop

$this->_select = '
        a.id_currency,
        a.id_order AS id_pdf,
        CONCAT(LEFT(c.`firstname`, 1), \'. \', c.`lastname`) AS `customer`,
        osl.`name` AS `osname`,
        os.`color`,
        IF((SELECT so.id_order FROM `'._DB_PREFIX_.'orders` so WHERE so.id_customer = a.id_customer AND so.id_order < a.id_order LIMIT 1) > 0, 0, 1) as new,
        country_lang.name as cname,
        IF(a.valid, 1, 0) badge_success';

        $this->_join = '
        LEFT JOIN `'._DB_PREFIX_.'customer` c ON (c.`id_customer` = a.`id_customer`)
        INNER JOIN `'._DB_PREFIX_.'address` address ON address.id_address = a.id_address_delivery
        INNER JOIN `'._DB_PREFIX_.'country` country ON address.id_country = country.id_country
        INNER JOIN `'._DB_PREFIX_.'country_lang` country_lang ON (country.`id_country` = country_lang.`id_country` AND country_lang.`id_lang` = '.(int)$this->context->language->id.')
        LEFT JOIN `'._DB_PREFIX_.'order_state` os ON (os.`id_order_state` = a.`current_state`)
        LEFT JOIN `'._DB_PREFIX_.'order_state_lang` osl ON (os.`id_order_state` = osl.`id_order_state` AND osl.`id_lang` = '.(int)$this->context->language->id.')';
        $this->_orderBy = 'id_order';
        $this->_orderWay = 'DESC';
        $this->_use_found_rows = true;