MYSQL数据+ PHP到FLOTgraphing

im quite new to mysql and flot graphing, but i get the general idea. This is my scenario: I receive data from a device, in which i put into mysql database. am i wrong in saying that the new data will replace the existing data in the database? i then need to plot that on a graph, how do i get(store) the old values so i can put in the data in this line?

 $(function () {
    var d4 = [[36,37],[50,51],null,[23,24],[18,17]];
    $.plot($("#placeholder"), [d4]);
  });

if not, i'll only be getting the current data... and that doesnt give me a line.. it'll give me datapoints haha Thanks for your help!

First, you'll want to set the stage for a graph that you can recreate dynamically. To do so, grab your container then fire off an ajax call to the script that wraps up your data. Within the ajax success call, catch the script's results within a function and send it off to a method such as resetGraph that will reset the graph according to the new information found within the database.

var dataview = $("#placeholder");
$.ajax({
    url: "index.php",
    data: "stuff&junk&things",
    method: 'GET',
    dataType: 'json',
    success: function(msg){
        resetGraph(msg);
    }
});

function resetGraph( data ){

    plot = $.plot(dataview, data.data, {
        points: { show: true, radius: 5 },
        xaxis: { ticks: data.ticks, tickSize: 7 },
        yaxis: {labelHeight: 2}
    });

}

Your script should be populating arrays with the necessary information then json_encoding it before sending it back to Jquery. For example,

echo json_encode( 
    array( 
        "data" => array(
            array("data" => array(1,2,3))
        ),
        "ticks" => array(2, "two")
    )
);