如何使用DynamoDB PHP从表中获取最新的时间戳值

现在我要显示“如果用户已登录他的帐户,我应该为每个传感器显示所有传感器的最新时间戳值”.

我做了三个查询,例如“我在他的帐户下获取了所有设备 – >原始传感器ID – >每个传感器最新值”,因此这个过程需要很长时间才能执行.

我的表看起来像这样：

用户：

---------------------
|sno  | userId      |
---------------------
| 1   | naveenkumar |
|--------------------
| 2   | abc         |
|--------------------
| 3   | xyz         |
|--------------------

sensor_devices：

---------------------
| id | sensorId     |
---------------------
| 1  | sensor1      |
|--------------------
| 2  | sensor2      |
|--------------------
| 3  | sensor3      |
|--------------------
| 4  | sensor4      |
---------------------
| 5  | sensor5      |
---------------------

和

用户传感器：

----------------------
| userId | sensorId  |
----------------------
| 1      |  1        |
|---------------------
| 1      |  2        |
|---------------------
| 1      |  4        |
|---------------------
| 2      |  5        |
|---------------------

data_tbl：

---------------------------------------------
| sensorId  | value    | timestamp          |
---------------------------------------------
| sensor1   | 4.3      | 2014-01-21 11:21:00|
|--------------------------------------------
| sensor2   | 5.0      | 2014-01-21 11:22:00|
|--------------------------------------------
| sensor3   | 10.0     | 2014-01-21 11:19:00|
|--------------------------------------------
| sensor4   | 6.3      | 2014-01-21 11:25:00|
|--------------------------------------------
| sensor1   | 8.3      | 2014-01-21 11:26:00|
|--------------------------------------------
| sensor2   | 6.0      | 2014-01-21 11:27:00|
|--------------------------------------------
| sensor3   | 9.0      | 2014-01-21 11:24:00|
|--------------------------------------------
| sensor4   | 6.3      | 2014-01-21 11:30:00|
|--------------------------------------------

和最终输出表将在他的主页上看到用户：

---------------------------------------------
| sensorId  | value    | timestamp          |
---------------------------------------------
| sensor1   | 8.3      | 2014-01-21 11:26:00|
|--------------------------------------------
| sensor2   | 6.0      | 2014-01-21 11:27:00|
|--------------------------------------------
| sensor4   | 6.3      | 2014-01-21 11:30:00|
|--------------------------------------------

我的查询看起来像这样,并且需要很长时间才能执行,所以请为我提供更好的解决方案：

我们假设$_SESSION [‘login_id’] = 1;

<?php
  $aws = Aws::factory('config.php');
  $client = $aws->get("dynamodb");

  $tableName = "data_tbl";
  echo "<table border=1>";
  echo "<tr>";

  echo "<th>Sensor ID</th>";
  echo "<th>value</th>";
  echo "<th>Timestamp</th>";
  echo "</tr>";

  //Query to get user devices
  $devices = $client->query(array(
    "TableName" => "users-sensors","KeyConditions" => array(
      "userId" => array(
        "ComparisonOperator" => ComparisonOperator::EQ,"AttributeValueList" => array(
          array(Type::STRING => $_SESSION['login_id'])
        )
      )
    )
  ));
  foreach ($devices['Items'] AS $key=>$value) {
    $id = $value['sensorId']['S'];
    //Query to get original sensorId from sensor serial number
    $device = $client->query(array(
      "TableName" => "sensor_devices","KeyConditions" => array(
        "id" => array(
          "ComparisonOperator" => ComparisonOperator::EQ,"AttributeValueList" => array(
            array(Type::STRING => $id)
          )
        )
      )
    ));
    $dids =  $device['Items'][0]['sensorId'][Type::STRING];
    //Query to get all latest values of sensors
    $response = $client->query(array(
      "TableName" => $tableName,"KeyConditions" => array(
        "sensorId" => array(
          "ComparisonOperator" => ComparisonOperator::EQ,"AttributeValueList" => array(
            array(Type::STRING => $dids)
          )
        )
      ),"Select" => "SPECIFIC_ATTRIBUTES","AttributesToGet" => array("sensorId","value","timestamp"),"ScanIndexForward" => false,"Limit" => 1  
    ));
    foreach ($response['Items'] AS $key=>$value) {
      echo "<tr>";
      $link = "graph.php?id=".$id;
      echo "<td><a href='$link'>".$value['sensorId']['S']."</a></td>";
      echo "<td><a href='$link'>".$value['value']['S']."</a></td>";
      $epoch = $value['timestamp']['S'];
      $timestamp = date('Y-m-d H:i:s',$epoch);
      echo "<td><a href='$link'>".$timestamp."</a></td>";
      echo "</tr>";
    }
  }
  echo "</table>";
?>

如果我能得到答案,我会完成我的工作.
谢谢