<?php
    error_reporting(E_ALL);
    ini_set('display_errors', 1);
?>

<div id="container">
    <ul class="nav">
        <li><a href="index.php">home</a></li>
        <li>
          <a href="#" id="destinations">destinations</a>
<div id="subMenu">
<?php
    $servername = "localhost:3306";
    $username = "root";
    $password = "";
    $dbname = "site_comboios";

    //Abre ligação à BD
    $mysqli = new mysqli($servername, $username, $password, $dbname);

//check connection
if($mysqli->connect_errno) {
    echo 'Error connecting to database';
    exit();
         }

//show sub-menu
$query = "SELECT * FROM continentes ORDER BY id";
$result = mysqli_query($mysqli, $query);
    while ($row = mysqli_fetch_assoc($result)) {
          $Cont = $row['continente'];
echo "<div class='nav-column'><a href='#cnt_submenu' data-id='<?php   $query ?>' class='continente'>" .($Cont). "</a></div> ";
        }
 ?>

 </div>
    </li>
    <li><a href="#about">about</a></li>
    <li><a href="#contact">contact</a></li>
  </ul>
 </div>

<div id="cnt_submenu" data-id="divSub" class="submenu_continente  active">
<?php
//retrieve european countries from DB and open <ul> with 9 results
$conn = mysqli_connect("localhost:3306","root","","site_comboios");
$sql_eurCountries = "SELECT * FROM countries ORDER BY id WHERE   id_continentes = 1";
$result_eurCountries = mysqli_query($conn, $sql_eurCountries);

if($result_eurCountries > 0) {
    while ($row_eurCountries = mysqli_fetch_assoc($result_eurCountries))   {
    $país_Eur = $row_eurCountries['id_continentes'];
    echo "<ul><li><a href='#'>". $país_Eur ."</a>";
}

} else if ($result_eurCountries == 9) {
       echo '</li></ul>';
       }
?>
<span class="close">x</span>
</div>

<div id="cnt_submenu" data-id="divSub" class="submenu_continente active">
<?php
//retrieve african countries from DB
$sql_afrCountries = "SELECT * FROM countries ORDER BY id WHERE   id_continentes = 2";
$result_afrCountries = mysqli_query($conn, $sql_afrCountries);

while ($row_afrCountries = mysqli_fetch_assoc($result_afrCountries)) {
     $pais_Afr = $row_afrCountries['id_continentes'];
     echo "<ul><li><a href='#'>". $pais_Afr ."</a></li></ul>";
      }
 ?>
 </div>

<div id="cnt_submenu" data-id="divSub" class="submenu_continente active">
<?php
//retrieve asian countries from DB
$sql_asiaCountries = "SELECT * FROM countries ORDER BY id WHERE  id_continentes = 3";
$result_asiaCountries = mysqli_query($conn, $sql_asiaCountries);

if($sql_asiaCountries == FALSE) {
      die(mysqli_errno($conn));
      }

while ($row_asiaCountries = mysqli_fetch_assoc($result_asiaCountries)) {
      $pais_Asia = $row_asiaCountries['id_continentes'];
      echo "<ul><li><a href='#'>". $pais_Asia ."</a></li></ul>";
      }

?>
</div>

<div id="cnt_submenu" data-id="divSub" class="submenu_continente active">
<?php
//retrieve oceania countries from DB
$sql_oceaCountries = "SELECT * FROM countries ORDER BY id WHERE id_continentes = 4";
$result_oceaCountries = mysqli_query($conn, $sql_oceaCountries);

if($sql_oceaCountries == FALSE) {
       die(mysqli_errno($conn));
      }

while ($row_oceaCountries = mysqli_fetch_assoc($result_oceaCountries)) {
    $pais_Oceania = $row_oceaCountries['id_continentes'];
    echo "<ul><li><a href='#'>". $pais_Oceania ."</a></li></ul>";
      }
?>
</div>

<div id="cnt_submenu" data-id="divSub" class="submenu_continente  active">
<?php
//retrieve north america countries from DB
$sql_norCountries = "SELECT * FROM countries ORDER BY id WHERE  id_continentes = 5";
$result_norCountries = mysqli_query($conn, $sql_norCountries);

if($sql_norCountries == FALSE) {
    die(mysqli_errno($conn));
    }

while ($row_norCountries = mysqli_fetch_assoc($result_norCountries)) {
$pais_North = $row_norCountries['id_continentes'];
echo "<ul><li><a href='#'>". $pais_North ."</a></li></ul>";
}
?>
</div>

<div id="cnt_submenu" data-id="divSub" class="submenu_continente  active">
<?php
//retrieve south america countries from DB
$sql_sulCountries = "SELECT * FROM countries ORDER BY id WHERE  id_continentes = 6";
$result_sulCountries = mysqli_query($conn, $sql_sulCountries);

if($sql_sulCountries == FALSE) {
      die(mysqli_errno($conn));
     }

while ($row_sulCountries = mysqli_fetch_assoc($result_sulCountries)) {
      $pais_South = $row_sulCountries['id_continentes'];
      echo "<ul><li><a href='#'>". $pais_South ."</a></li></ul>";
}
?>
</div>

$('.continente').hover(function(){
    var subCountry = $(this).data('id');
    $('divSub').show(subCountry);
        });

SELECT * FROM countries ORDER BY id WHERE   id_continentes = 1

SELECT * FROM countries WHERE id_continentes = 1 ORDER BY id