php代码来检查当前日期并将当前时间戳插入mySQL

<?php
if($_SERVER['REQUEST_METHOD']=='POST'){
 $staffID = $_POST['staffID'];
date_default_timezone_set("Asia/Singapore");
$checkInTime = $_SERVER['REQUEST_TIME'];
 $today = date('Y-m-d');
require_once('dbconnect.php');
$sqlcheck = "SELECT * FROM StaffAttendacne WHERE StaffID = '$staffID' AND Date ='$today'";
$sql = "INSERT INTO StaffAttendance (StaffID,Date,CheckInTime) VALUES ('$staffID','$today','$checkInTime')";
$result = mysqli_query($con,$sqlcheck);
 $check = mysqli_fetch_array($result);
if (isset($check)){
 echo "You have already checked in";
 }else {
 echo"$checkInTime";
 mysqli_query($con,$sql);
 }

如何将 PHP 插入签入时间(插入时间戳(写入 SQL 数据库。时间是应用程序启动的时间。我已经编写了这段代码，但没有工作