<form id="task-form">
                <div class="form-group">
                  <input type="number" id="id" placeholder="codigo" class="form-control">
                </div>
                <div class="form-group">
                  <input type="number" id="cantidad" placeholder="cantidad" class="form-control">
                </div>
                <button type="submit" class="btn btn-primary btn-block text-center">
                  Agregar
                </button>
              </form>


        <div class="col-md-7">
       <div class="bg-white">
          <table class="table table-bordered table-sm">
            <thead>
              <tr>
                <td>N°</td>
                        <td>Codigo</td>
                <td>Producto</td>
                <td>Cantidad</td>
                        <td>Precio</td>
                <td>Total</td>
              </tr>
            </thead>
            <tbody id="tasks"></tbody>
          </table>
        </div>
      </div>

include('conec.php');

$id = $_POST['id'];

$query = "SELECT * from productos WHERE id_prod=$id";
$result = mysqli_query($con, $query);



  if(!$result) {
die('Query Failed'. mysqli_error($con));
}

$json= array();

while($row = mysqli_fetch_array($result)) {
$json[] = array(
    'id' => $row['id_prod'],
    'nombre' => $row['nombre_prod'],
    'precio' => $row['precioV_prod'],
    'cantidad' => $cantidad,
    'total' => (($cantidad)*($row['precioV_prod']))
);
}

$jsonstring = json_encode($json);
echo $jsonstring;