if (isset($_POST["id_requests"])){
             $id = mysql_real_escape_string($_POST['id_requests']);
             $them = mysql_real_escape_string($_POST['theme']);
             $m_fio = mysql_real_escape_string($_POST['master']);
                         
             $q=mysql_query("UPDATE t_requests SET t_requests.theme='{$them}', t_requests.id_master='{$m_fio}'  WHERE t_requests.id_requests='{$id}'");
             if (!$q) {
                echo "Не удалось выполнить запрос SQL";
                }
             }

$id_requests = $_GET['id_requests'];
 if (isset ($id_requests)){
              
    $result = mysql_query("SELECT req.id_requests, req.theme, req.description, req.author_fio, master.last_name_master
     LEFT JOIN t_master master ON req.id_master = master.id_master
      WHERE req.id_requests=".$id_requests);
                    
     $new = mysql_fetch_array($result);
     echo "<tr >
        <td> Тема:</td>
        <td>
                <input type='text' name='theme' value=".$new["theme"]." 
       </td>      
    </tr>   
    <tr>         
       <td>Мастер:</td>
       <td>
    <select> "
    .$result1 = mysql_query("select * from t_master");
    while($master=mysql_fetch_array($result1)){
    echo "<option >".$master["last_name_master"]." </option>";}
    "</select>
    <input type='hidden' name='master' value=".$master["id_master"].">
</td>