Php 谷歌图表：对象2013-07-25没有方法'；获得时间

我正在尝试用GoogleCharts API绘制图表。一列包含日期，另一列包含数字

这是获取我的数据的php页面：

<?php
include 'core/init.php';

$result = mysql_query('SELECT amountDone, resultDate FROM result');

$table = array();
$table['cols'] = array(
    array('label' => 'Done', 'type' => 'number'),
    array('label' => 'Date', 'type' => 'date')
);

$rows = array();
while($r = mysql_fetch_assoc($result)) {
    $temp = array();
    $temp[] = array('v' => (int)$r['amountDone']);
    $temp[] = array('v' => $r['resultDate']);
    $rows[] = array('c' => $temp);
}

$table['rows'] = $rows;

$jsonTable = json_encode($table);

echo $jsonTable;

?>

在我的主页中，我尝试用以下代码绘制图表：

<script type="text/javascript">

        // Load the Visualization API and the piechart package.
        google.load('visualization', '1', {'packages':['corechart']});

        // Set a callback to run when the Google Visualization API is loaded.
        google.setOnLoadCallback(drawChart);

        function drawChart() {
          var jsonData = $.ajax({
              url: "get_json.php",
              dataType:"json",
              async: false
              }).responseText;

          // Create our data table out of JSON data loaded from server.
          var data = new google.visualization.DataTable(jsonData);

          // Instantiate and draw our chart, passing in some options.
          var chart = new google.visualization.ColumnChart(document.getElementById('chart_div'));
          chart.draw(data, {width: 400, height: 240});
        }

</script>

有人知道这意味着什么吗？因为我没有任何其他错误

提前谢谢

将我的查询更改为：

$result = mysql_query("SELECT DATE_FORMAT(resultDate, '%W, %D %M %Y') as Datum,    SUM(amountDone) as AmountD, SUM(amountToDo) as AmountT
                       FROM result
                       GROUP BY resultDate");

现在类型是string。工作起来很有魅力。：）

Object 2013-07-25 has no method 'getTime

$result = mysql_query("SELECT DATE_FORMAT(resultDate, '%W, %D %M %Y') as Datum,    SUM(amountDone) as AmountD, SUM(amountToDo) as AmountT
                       FROM result
                       GROUP BY resultDate");