如何解决查询两次插入数据库的问题？

Question

image from phpmyadmin (twice inserted)我的目标是向数据库插入<form>并将开始日期/时间和结束日期/时间。单击日历后，开始日期/时间和结束日期/时间将被插入数据库，然后将弹出一个模态（预订表格）。单击模式中的提交按钮后，现在将插入数据库中，但没有开始日期/时间和结束日期/时间。我正在使用fullcalendar.io

$title = mysqli_real_escape_string($conn, $_REQUEST['title']);
$facility = mysqli_real_escape_string($conn, $_REQUEST['facility']);
$participants = mysqli_real_escape_string($conn, $_REQUEST['participants']);
$start_event = mysqli_real_escape_string($conn, $_REQUEST['start']);
$end_event = mysqli_real_escape_string($conn, $_REQUEST['end']);

$query = "INSERT INTO reservation (title, Venue, start_event, end_event, 
Participants) VALUES ('$title', '$facility', '$start_event', 
'$end_event', '$participants')";

if(isset($_POST["submit"])){

if ($conn->query($query) === TRUE) {
    header("location: homepage_client_calendar.php");
    } else {
        echo "Error: " . $query . "<br>" . $conn->error;
    }
}
$conn->close();

这是日历代码

if(btn.onclick()){
var start = $.fullCalendar.formatDate(start, "Y-MM-DD HH:mm");
var end = $.fullCalendar.formatDate(end, "Y-MM-DD HH:mm");
$.ajax({
     url:"insert_calendar.php",
     type:"POST",
     data:{start:start, end:end},
     success:function()
    {
      calendar.fullCalendar('refetchEvents');
      // alert("Added Successfully");
    }
    })
}