获取当月第一天和最后一天

// 返回当前月第一天和最后一天
function getthemonth($date)
{
  $firstday = date('Y-m-01', strtotime($date));
  $lastday = date('Y-m-d', strtotime("$firstday +1 month -1 day"));
  return array($firstday,$lastday);
}

//使用
$today = date("Y-m-d");
$day=getthemonth($today);
echo "当月的第一天: ".$day[0].' 00:00:00.000'." 当月的最后一天: ".$day[1].' 23:59:59:998';
echo "
";
exit;

Sqlserver：datetime类型的精度（不确定性）问题
https://www.cnblogs.com/password1/p/6994601.html

PHP获取当月天数及当月第一天及最后一天(计划任务常用)
https://blog.csdn.net/qq_42154707/article/details/86503662