public function get_list_of_product_info($data = NULL)
 {
     $sqlbuilder = new SQLBuilder();
     if (is_null($data)) {
         $sql = mysqli_query($this->db, $sqlbuilder->get_list_of_product_info());
     } else {
         $sql = mysqli_query($this->db, $sqlbuilder->alter_product_query($data));
     }
     $result = NULL;
     if ($sql && mysqli_num_rows($sql) != 0) {
         $result = array();
         while ($rlt = mysqli_fetch_array($sql, MYSQL_ASSOC)) {
             $result[] = $rlt;
         }
     }
     return $result;
 }