$query = $mysqli->query("SELECT `contest_id`, `type_operation`, `name_val`, `name_prod`, `price`, SUM(`amount`) as amount , `total`, `dttm_create_order`, `dttm_close_order`, `status` FROM (SELECT `contest_id`, `type_operation`, `name_val`, `name_prod`, `price` , `amount` as amount , `total` , `dttm_create_order`, `dttm_close_order`, `status` FROM `bitorders` UNION SELECT `contest_id`, `type_operation`, `name_val`, `name_prod`, `price`, `amount` as amount , `total`, `dttm_create_order`, `dttm_close_order`, `status` FROM `orders` ) as tableobsh WHERE `name_prod`= 'aaa' AND status = 0 GROUP BY price , type_operation ORDER BY price " );

    while ($row = $query->fetch_assoc()) {
        //$orderbook['order_id'][]      = $row['order_id'];
        $orderbook['price'][]      = $row['price']/100000000;
        //$orderbook['user_id'][]      = $row['user_id'];
        $orderbook['contest_id'][]      = $row['contest_id'];
        $orderbook['type_operation'][]   = $row['type_operation'];
        $orderbook['name_val'][]  = $row['name_val'];
        $orderbook['name_prod'][]   = $row['name_prod'];
        $orderbook['amount'][]    = $row['amount']/100000000;
        $orderbook['total'][]     = $row['total']/100000000;
        $orderbook['dttm_create_order'][]    = $row['dttm_create_order'];
        $orderbook['dttm_close_order'][]      = $row['dttm_close_order'];
        $orderbook['status'][]      = $row['status'];

    }
    $out = array(
        'orderbook' => $orderbook
    );

WHERE `name_prod`= 'aaa'

$coins = array('aaa', 'bbb', 'ccc');
WHERE `name_prod` IN (" . implode(',', $coins) . ")