====== จะทำ 3 level dropdown โดยดึงจาก DB ค่ะ ======

<table width="517" border="1">
  <tr>
    <td width="87">Source:</td>
    <td width="414"><? echo'<select name="source" onChange="showUser(this.value)"><option value="">--Select--</option>';

$res=mysql_query("SELECT DISTINCT sector FROM `contents_travel`");
if(mysql_num_rows($res)==0) echo "there is no data in table..";
else
while ($row=mysql_fetch_assoc($res)) {
    echo"<option value=" . $row['sector'] . ">" . $row['sector'] . "</option>";
    }
echo'</select>' ?></td>
  </tr>
  <tr>
    <td>School:</td>
    <td><? echo'<select name="school" onChange="showUser(this.value)"><option value="">--Select--</option>';

$res=mysql_query("SELECT DISTINCT province FROM `contents_travel` WHERE sector='$source' ");
if(mysql_num_rows($res)==0) echo "there is no data in table..";
else
while ($row=mysql_fetch_assoc($res)) {
    echo"<option value=" . $row['province'] . ">" . $row['province'] . "</option>";
    }
echo'</select>' ?></td>
  </tr>
  <tr>
    <td>Program:</td>
    <td><? echo'<select name="sub" onChange="showUser(this.value)"><option value="">--Select sub--</option>';

$res=mysql_query("SELECT DISTINCT area FROM `contents_travel` WHERE province ='$province'");
if(mysql_num_rows($res)==0) echo "there is no data in table..";
else
while ($row=mysql_fetch_assoc($res)) {
    echo"<option value=" . $row['area'] . ">" . $row['area'] . "</option>";
    }
echo'</select>' ?></td>
  </tr>
</table>