สอบถามปัญหา ajax รับค่าจาก php แบบไม่มีการ action หรือ กดปุ่มใดๆ

<table class="table table-bordered table-striped">
    <thead>
     <tr>
      <th width="10%">ID</th>
      <th width="40%">Name</th>
      <th width="10%">Gender</th>
      <th width="30%">Designation</th>
      <th width="10%">Age</th>
     </tr>
    </thead>
    <tbody id="employee_data">
    </tbody>
   </table>

function fetch_employee_data()
 {
  $.ajax({
   url:"fetch.php",
   method:"POST",
   dataType:"json",
   success:function(data)
   {
    for(var count=0; count<data.length; count++)
    {
     var html_data = '<tr><td>'+data[count].id+'</td>';
     html_data += '<td data-name="name" class="name" data-type="text" data-pk="'+data[count].id+'">'+data[count].name+'</td>';
     html_data += '<td data-name="gender" class="gender" data-type="select" data-pk="'+data[count].id+'">'+data[count].gender+'</td>';
     html_data += '<td data-name="designation" class="designation" data-type="text" data-pk="'+data[count].id+'">'+data[count].designation+'</td>';
     html_data += '<td data-name="age" class="age" data-type="text" data-pk="'+data[count].id+'">'+data[count].age+'</td></tr>';
     $('#employee_data').append(html_data);
    }
   }
  })
 }

<?php
//fetch.php
$connect = mysqli_connect("localhost", "root", "", "testing");
$query = "SELECT * FROM employee WHERE key=$_GET['key']";  <------------เอาค่า   $_GET['key']  มาเป็นเงือนไขตรงนี้ 
$result = mysqli_query($connect, $query);
$output = array();
while($row = mysqli_fetch_assoc($result))
{
 $output[] = $row;
}
echo json_encode($output);
?>