Charts and graphs with jplot, jQuery and php

For rendering charts in one of my projects, I started using jplot library.

Usage is pretty simple, but I needed some specifics in implementation.
First, add the following lines to HEAD section:

In my case, I used also date rendering and some more features, provided by jplot.

Then I added the following code to my page:

    ...
    Option 1
    Option 2
    Option 3

I used such construction in order to dynamically return reports on needed options.

My javascript code is following:

$(function() {
var plot2 = "";

    $('select#price').change(function() {
        if (plot2) plot2.destroy(); //this string is needed to make sure, that old chart is not displayed while new is generated
        var id = $(this).val(); // here we get selected option value
        var name = $("#price option[value='" + id + "']").text(); // here we take the name of option, selected.

        $.getJSON("/lib/helpers/price_data.php?price_code=" + id, //read JSON data from helper script
            function (data) {
                plot2 = $.jqplot('chart_display', [data], {
                    title: name,
                    axes:{
                        xaxis:{
                            renderer:$.jqplot.DateAxisRenderer, // X axis will be rendered as date
                            tickOptions:{
                                formatString: '%b %#d' // format of date display
                            }
                        },
                        yaxis:{
                            tickOptions:{
                                formatString:'%.2f EUR' // format of price display
                            }
                        }
                    },
                    series:[
                        {lineWidth:4, markerOptions:{style:'square'}} // one of the features to display break points
                    ],
                    highlighter: {
                        show: true // mouse hover highlighting on break points
                    },
                    cursor: {
                        show: false,
                        tooltipLocation:'sw' // mouse hover tooltip onbreak points
                    }
                });
            })
    });
});

To display correctly all these data, we need correct data to be returned by our php script. In my case it should be in format of JSON data [[‘2008-09-30 4:00PM’,4], [‘2008-10-30 4:00PM’,6.5], [‘2008-11-30 4:00PM’,5.7], [‘2008-12-30 4:00PM’,9], [‘2009-01-30 4:00PM’,8.2]]

For this purpose, I generate output of script in the following way:

$query = mysql_query("SELECT * FROM prices WHERE price_code = '$price_code' ORDER BY date") or die(mysql_error());
while ($row = mysql_fetch_array($query))
{
     $result[] = array($row['date'].' 0:00AM', round($row['price']));
}
print json_encode($result);