Google chart "Table has no columns"

Your loadData function doesn't return anything, so the json variable is null. I would suggest a slight reorganization of your code to get the effect you want:

function drawChart (json) {    var data = new google.visualization.DataTable(json);    var options = {        vAxis: {minValue: 0}    };    var chart = new google.visualization.AreaChart(document.getElementById('chart_div'));    chart.draw(data, options);}function loadData () {    var request=new XMLHttpRequest();    request.onreadystatechange = function() {        if (request.readyState == 4 && request.status == 200) {            drawChart(request.responseText);        }    }    request.open("GET","testsrun.php?json=true&branch=test",true);    request.send();}google.load('visualization', '1', {packages:['corechart'], callback: loadData});

Also, the numbers in your JSON are being input as strings, which will cause problems with your charts. You need to input them as numbers, eg. {"v":"0"} should be {"v":0}. If you are using PHP's json_encode function to build your JSON, you can pass JSON_NUMERIC_CHECK as a second argument to the function call to make sure your numbers are input correctly:

json_encode($myData, JSON_NUMERIC_CHECK);