how to get one value of checkbox

how for me to get one value of checkbox if i checked two checkbox, so i can make warn when i want to edit category. only need one value to be PrimaryKey for edit category.

 $query="select * from category";
 $query_exec = mysqli_query($conn, $query) or die(mysqli_error($conn));
 while($data = mysqli_fetch_array($query_exec))
 {
 echo"<tr>";
 echo"<td>"."<input type='checkbox' name='check_list[]' value='".$data['kode_kategori']."'/>"."</td>";
 echo"<td id='width_txt'>".$data["kode_kategori"]."</td>";
 echo"<td id='width_txt'>".$data["nama_kategori"]."</td>";
 echo"<td id='width_txt'>".$data["inisial_produk"]."</td>";
 echo"<td id='width_txt'>".$data["status_kategori"]."</td>";        
 echo"</tr>";
 }
 <td><input type="submit" name="edit" value="Edit" /></td>
 <?php
 if(isset($_POST['edit']))
 {
   $check_list = $_POST['check_list'];
   if(empty($_POST['check_list']))
   {
     echo ("<script language='javascript'>
     alert('Pls checklist first.');
     </script>");
   }
   else
   {
     $n = count($check_list);
     foreach($check_list as $check)
     {
       for($i=0; $i < $n; $i++)
       {
          if($i == 0)
          {
             echo ("<script language='javascript'>                              
             window.location='http://ift.tt/1StF1O5';
              </script>");
          }
           else
           {
             echo ("<script language='javascript'>
             alert('Only need one value.');
             </script>");
           }
        }
    }
  }
  }
 ?> 

So this is it the code..