opencart did not execute correct mysql query - php

Question

I add a new column in orders table (shopper_id) I am trying to get the data with the new column condition but result returns empty
the query is correct and when I execute it directly it returns correct results
open cart formula
SELECT o.order_id, o.firstname, o.lastname, os.name as status, o.date_added,o.shopper_id as shopper_id , o.total, o.currency_code, o.currency_value FROM `" . DB_PREFIX . "order` o LEFT JOIN " . DB_PREFIX . "order_status os ON (o.order_status_id = os.order_status_id) WHERE o.store_id = '" . (int) $store_id . "' AND o.order_status_id = '" . (int) $status . "' AND os.language_id = '" . (int) $this->config->get('config_language_id') . "' AND ( o.shopper_id = NULL OR o.shopper_id = '0' ) ORDER BY o.order_id DESC
Below is my mysql query-
SELECT o.order_id, o.firstname, o.lastname, os.name as status, o.date_added,o.shopper_id, o.total, o.currency_code, o.currency_value FROM `medrahoc_order` o LEFT JOIN medrahoc_order_status os ON (o.order_status_id = os.order_status_id) WHERE o.store_id = '0' AND o.order_status_id = '1' AND os.language_id = '1' AND ( o.shopper_id = NULL OR o.shopper_id = 0 ) ORDER BY o.order_id DESC
my model function
public function getOrdersByStore($store_id, $status = null) {
if (isset($status)) {
$sql = "SELECT o.order_id, o.firstname, o.lastname, os.name as status, o.date_added,o.shopper_id as shopper_id , o.total, o.currency_code, o.currency_value FROM `" . DB_PREFIX . "order` o LEFT JOIN " . DB_PREFIX . "order_status os ON (o.order_status_id = os.order_status_id) WHERE o.store_id = '" . (int) $store_id . "' AND o.order_status_id = '" . (int) $status . "' AND os.language_id = '" . (int) $this->config->get('config_language_id') . "' AND o.shopper_id = '0' ORDER BY o.order_id DESC";
} else {
$sql = "SELECT o.order_id, o.firstname, o.lastname, os.name as status, o.date_added, o.total, o.currency_code, o.currency_value FROM `" . DB_PREFIX . "order` o LEFT JOIN " . DB_PREFIX . "order_status os ON (o.order_status_id = os.order_status_id) WHERE o.store_id = '" . (int) $store_id . "' AND o.order_status_id > '0' AND os.language_id = '" . (int) $this->config->get('config_language_id') . "' ORDER BY o.order_id DESC";
}
$query = $this->db->query($sql);
return $query->rows;
}