如何解决：JSON编码的mysqli查询不显示任何数据

Question

我正在尝试查询数据库，并且JSON对结果进行编码。我正在使用以下代码：

    <?php
        $db_name="database";
        $mysql_user="access";
        $mysql_pass="accesspass";
        $server_name="localhost";

        $connection = mysqli_connect($server_name, $mysql_user, $mysql_pass, $db_name);

        $query = 'SELECT * FROM deals d, restaurants r WHERE d.res_id = r.res_id ORDER BY deal_id ASC';
        $result = mysqli_query($connection, $query);

        $json_array = array();

        if(mysqli_num_rows($result) > 0) {
            while($row = mysqli_fetch_assoc($result)){
                $json_array[]=$row;
            }
         } else {
            echo "Unable to retrieve results from database.";
        }

        echo json_encode($json_array);
    ?>

我希望它以以下格式显示结果： {“交易”：[{...}，{...}，{...}]} 但是，它什么也没显示。