Column Chart: All series on a given axis must be of the same data type - google-visualization

Question

What am i doing wrong with the following code to get an error All series on a given axis must be of the same data type
function drawVisualization(){
var performanceJson = $.ajax({
url : "{% url json_data %}",
type:"GET",
dataType: "json",
cache: false,
async: false}).responseJSON;
var performanceData = new google.visualization.DataTable();
performanceData.addColumn('string', 'Question');
performanceData.addColumn('string', 'Headings');
performanceData.addColumn('number', 'TotalScore');
performanceData.addColumn('number', 'Score');
performanceData.addRows(performanceJson);
var performanceOptions = {
title : 'Performance Report',
subtitle: 'Based on a scale of 1 to 7',
hAxis : {title:'Question', titleTextStyle:{color:'red'}},
vAxis : {title:'Scores'},
};
var chart = new google.visualization.ColumnChart(document.getElementById('chart_div'));
chart.draw(performanceData, performanceOptions);
}
The performanceJson variable has the value:
[["No. of people", "Area", 6, 1], ["Scholars", "Standard", 12, 2], ["Co-ordination", "Standard", 18, 14]]

Answer 1

For a ColumnChart all columns(except the first) have to be of type number.
Column #2 is of type string, column#3 and column #4 are of type number, so the error-message should be clear.
I'm not sure for what column #2 is good for, but you may not use this column as data-column
You may e.g. use this column as annotation:
google.load('visualization', '1', {packages: ['corechart', 'bar']});
google.setOnLoadCallback(drawVisualization);
function drawVisualization(){
var performanceJson = [["No. of people", "Area", 6, 1],
["Scholars", "Standard", 12, 2],
["Co-ordination", "Standard", 18, 14]];
var performanceData = new google.visualization.DataTable();
performanceData.addColumn('string', 'Question');
performanceData.addColumn({type:'string',role:'annotation'});
performanceData.addColumn('number', 'TotalScore');
performanceData.addColumn('number', 'Score');
performanceData.addRows(performanceJson);
var performanceOptions = {
title : 'Performance Report',
subtitle: 'Based on a scale of 1 to 7',
hAxis : {title:'Question', titleTextStyle:{color:'red'}},
vAxis : {title:'Scores'},
};
var chart = new google.visualization.ColumnChart(document.getElementById('chart_div'));
chart.draw(performanceData, performanceOptions);
}
<script type="text/javascript" src="https://www.google.com/jsapi"></script>
<div id="chart_div"></div>