$month = '04';
$year = '2017';
$max_day = cal_days_in_month(CAL_GREGORIAN, $month, $year);   //當月最后一天
//構造每天的數組
$days_arr = array();
for($i=1;$i=$max_day;$i++){
  array_push($days_arr, $i);
}
$return = array();
//查詢
foreach ($days_arr as $val){
  $min = $year.'-'.$month.'-'.$val.' 00:00:00';
  $max = $year.'-'.$month.'-'.$val.' 23:59:59';
  $sql = "select count(*) as total_num,sum(`total_price`) as amount from `orders` where `enterdate` >= {$min} and `enterdate` = {$max}";
  $return[] = mysqli_query($sql);
}
return $return;

$month = '04';
$year = '2017';
$max_day = cal_days_in_month(CAL_GREGORIAN, $month, $year);   //當月最后一天
$min = $year.'-'.$month.'-01 00:00:00';
$max = $year.'-'.$month.'-'.$max_day.' 23:59:59';
$sql = "select t.enterdate,count(*) as total_num,sum(t.total_price) as amount (select date_format(enterdate,'%e') as enterdate,total_price from orders where enterdate between {$min} and {$max}) t group by t.enterdate order by t.enterdate";
$return = mysqli_query($sql);