Submit ajax request on same page

if (isset($_SERVER['HTTP_X_REQUESTED_WITH']) && strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) === 'xmlhttprequest')
{
        //fun goes here.
}

Create a CSV File for a user in PHP

An improved version of the function from php.net

function download_csv_results($results, $name = NULL)
{
    if( ! $name)
    {
        $name = md5(uniqid() . microtime(TRUE) . mt_rand()). '.csv';
    }
    header('Content-Type: text/csv');
    header('Content-Disposition: attachment; filename='. $name);
    header('Pragma: no-cache');
    header("Expires: 0");
    $outstream = fopen("php://output", "w");
    fputcsv($outstream, array_keys($results[0])); //This will  include column headers
    foreach($results as $result)
    {
        fputcsv($outstream, $result);
    }
    fclose($outstream);
}

    require_once("yourdatabaseconnection.php");  //Include your database connection here
    $sql = mysql_query("SELECT * FROM your_table'") or die(mysql_error()); 

    if(mysql_num_rows($sql) > 0)
    {
        $results = array();
        while($rows = mysql_fetch_assoc($sql)){
            $results[] = $rows;   
        }
      //call your function here
       download_csv_results($results, 'your_file_name_here.csv');    }