MySQL DATE_ADD() vs php strtotime()

$l = 100;

 

// DATE_ADD() : 0 sec

$sql1 = "select * from TABLE where Date > DATE_ADD(NOW() INTERVAL -30 DAY)";
$starttime = time();
for ($i = 0; $i < $l; $i++) {
        mysql_query($sql1);
}
$endtime = time();
echo $endtime - $starttime, "\n";

 

// strtotime() : 7 sec

$date = date('Y-m-d H:i:s', strtotime('-30 days'));
$sql2 = "select * from TABLE where Date > '{$date}'";
$starttime = time();
for ($i = 0; $i < $l; $i++) {
        mysql_query($sql2);
}
$endtime = time();
echo $endtime - $starttime, "\n";