Fetching data drop down [closed]

The problem is when I click on the first class all classes data shown. I want when someone click on any class to only show that class data. I think the problemis in my query.

Here is my PHP code:

$x=$_POST['c_id'];
$sql = "select * from user1,classes where user1.clas=classes.c_id and id=id";
$resultset = mysqli_query($conn, $sql);
while( $rows = mysqli_fetch_array($resultset) ) { 
?>
   <tr>
      <td><?php echo  $rows['name'];?></td>
      <td><?php echo  $rows['class'];?></td>
   </tr>
<?php }?>

My JavaScript code:

function selectclass(){
   var x= document.getElementById("employee").value;
   $.ajax({
      url:"getstdata.php",
      method:"POST",
      data:{
         c_id: x
      },
      success:function(data){
         $("#ans").html(data)
      }       
   })
}

All I want clicking on drop down on any class only shows the all that class students.

source https://stackoverflow.com/questions/76901620/fetching-data-drop-down