日期

当日

date('Y-m-d")
date('Y-m-d 00:00:00')

取日期：年 月 日

date("Y", strtotime($startday))
date("m", strtotime($startday))
date("d", strtotime($startday))

上月 下月

$last_mont_first_date = date('Y-m-01 00:00:00',strtotime('last month'))
$next_mont_first_date = date('Y-m-20 00:00:00',strtotime('next month'))

2个日期比较大小的方法

protected function DateCompare($dateString1,$dateString2){
        $month1 = date("m", strtotime($dateString1));
        $month2 = date("m", strtotime($dateString2));
        $day1 = date("d", strtotime($dateString1));
        $day2 = date("d", strtotime($dateString2));
        $year1 = date("Y", strtotime($dateString1));
        $year2 = date("Y", strtotime($dateString2));
        $hour1 = date("H", strtotime($dateString1));
        $hour2 = date("H", strtotime($dateString2));
        $minute1 = date("i", strtotime($dateString1));
        $minute2 = date("i", strtotime($dateString2));
        $second1 = date("s", strtotime($dateString1));
        $second2 = date("s", strtotime($dateString2));
        $do1 = mktime($hour1, $minute1, $second1, $month1, $day1, $year1);
        $do2 = mktime($hour2, $minute2, $second2, $month2, $day2, $year2);
        if($do1<$do2){
            return '0';
        }
        if($do1==$do2){
            return '1';
        }
        if($do1>$do2){
            return '2';
        }
    }