How to download data in .csv format (php)

function export2csv(){
$file = 'export';

$result = mysql_query("SHOW COLUMNS FROM tbl ");
$i = 0;
if (mysql_num_rows($result) > 0) {
while ($row = mysql_fetch_assoc($result)) {
$csv_output .= $row['Field'].", ";
$i++;
}
}
$csv_output .= "\n";

$values = mysql_query("SELECT Colum1 , Colum 2  FROM tbl");
while ($rowr = mysql_fetch_row($values)) {
for ($j=0;$j<$i;$j++) {
$csv_output .= $rowr[$j].", ";
}
$csv_output .= "\n";
}

$filename = "filename_".date("Y-m-d_H-i",time());
header("Content-type: application/vnd.ms-excel");
header("Content-disposition: csv" . date("Y-m-d") . ".csv");
header( "Content-disposition: filename=".$filename.".csv");
print $csv_output;
}