MySQL クエリ結果を PHP で CSV に効率的にエクスポートするには?

SELECT * INTO OUTFILE "/path/to/file.csv"
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
LINES TERMINATED BY "\n"
FROM my_table;

$select = "SELECT * FROM my_table";
$export = mysql_query($select);
$fields = mysql_num_fields($export);

$header = '';
for ($i = 0; $i < $fields; $i++) {
    $header .= mysql_field_name($export, $i) . "\t";
}

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

header("Content-type: application/octet-stream");
header("Content-Disposition: attachment; filename=my_file.csv");
print "$header\n$data";