How to Efficiently Convert MySQL Query Results to CSV in PHP?

SELECT * INTO OUTFILE "c:/mydata.csv"
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
LINES TERMINATED BY "\n"
FROM my_table;

$select = "SELECT * FROM table_name";
$export = mysql_query ($select) or die ("Sql error : " . mysql_error());

$fields = mysql_num_fields ($export);
for ($i = 0; $i < $fields; $i++) {
    $header .= mysql_field_name($export, $i) . "\t";
}

while ($row = mysql_fetch_row($export)) {
    $line = '';
    foreach ($row as $value) {
        if (empty($value)) $value = "\t";
        else {
            $value = str_replace('"', '""', $value);
            $value = '"' . $value . '"' . "\t";
        }
        $line .= $value;
    }
    $data .= trim($line) . "\n";
}
$data = str_replace("\r", "", $data);

if ($data == "") $data = "\n(0) Records Found!\n";

header("Content-type: application/octet-stream");
header("Content-Disposition: attachment; filename=your_desired_name.xls");
header("Pragma: no-cache");
header("Expires: 0");
print "$header\n$data";