如何使用php提取select中的值?

I have this code here:

我这里有个代码:

if(isset($_POST['possible_new_dd'])){
    $dd = $_POST['possible_new_dd'];
    $id = $_POST['possible_new_dd_id'];
    $sql = mysqli_query($connection, "SELECT SUM(COILS),MACHINE, (SELECT COILS FROM ORDERS WHERE ID='$id') FROM ORDERS WHERE MACHINE=(SELECT MACHINE FROM ORDERS WHERE ID='$id') AND C_DD='$dd';");
    $row = mysqli_fetch_array($sql);
    $json->coils = $row['SUM(COILS)'];
    $json->machine = $row['MACHINE'];
    $json->new_coil = $row['?THE SELECT QUERY?'];
    $j = json_encode($json);
    echo$j;
}
if(isset($_