php实现比较两个字符串日期大小的方法

<?php
function dateBDate($date1, $date2) {
// 日期1是否大于日期2
 $month1 = date("m", strtotime($date1));
 $month2 = date("m", strtotime($date2));
 $day1 = date("d", strtotime($date1));
 $day2 = date("d", strtotime($date2));
 $year1 = date("Y", strtotime($date1));
 $year2 = date("Y", strtotime($date2));
 $from = mktime(0, 0, 0, $month1, $day1, $year1);
 $to = mktime(0, 0, 0, $month2, $day2, $year2);
 if ($from > $to) {
 return true;
 } else {
 return false;
 }
}
?>
$date1 = "2009-10-13";
$date= mktime(0, 0, 0, date("m", strtotime($date1)), date("d", strtotime($date1)), date("Y",strtotime($date1)));