Update dotaz ktery neupdatuje

<form class="form1" action="inf.php" method="post">
        <table>
          <tr>
            <td>Tvé uživatelské jméno je:</td>
            <td><?php echo( $_SESSION['username'])?></td>
          </tr>
          <tr>
            <td>Upravit e-mail:</td>
            <td><input type="text" placeholder="Zadej nový email" name="email_n"/></td>
          </tr>
          <tr>
            <td>Upravit věk:</td>
            <td><input type="number" placeholder="Zadej svůj věk" name="vek_n" /></td>
          </tr>
          <tr>
            <td>Upravit datum narození:</td>
            <td><input type="date"  name="datum_n" /></td>
          </tr>
          <tr>
            <td>&nbsp;</td>
            <td><input type="submit" value="Upravit" class="button" /></td>
          </tr>
        </table>
      </form>
      <?php
       $email_n = $_POST['email_n'];
       $vek_n = $_POST['vek_n'];
       $datum_n = $_POST['datum_n'];

       if(isset($email_n))
       {
        $update1 = "UPDATE inf SET  email= '".$email_n."' WHERE jmeno = '" . $_SESSION['username'] . "'";
        if ($db -> query($update1) === TRUE)
        {
         echo('<script> alert ("Řádek byl upraven")</script>');
        }
        else
        {
         echo('<script> alert ("Řádek nebyl upraven")</script>'); 
        }
       }

<?php
       $email_n = $_POST['email_n'];
       $vek_n = $_POST['vek_n'];
       $datum_n = $_POST['datum_n'];
       $tvejmeno_n = $_POST['tvejmeno_n'];
       $prijmeni_n = $_POST['prijmeni_n'];

       if(isset($tvejmeno_n))
       {
        $update1 = "UPDATE inf SET  tvejmeno= '". $tvejmeno_n ."' WHERE jmeno = '" . $_SESSION['username'] . "'";
        if ($db -> query($update1) === TRUE)
        {
         echo('<script> alert ("Řádek byl upraven")</script>');
        }
        else
        {
         echo('<script> alert ("Řádek nebyl upraven")</script>'); 
        }
       }
       else if(isset($prijmeni_n))
       {
        $update2 = "UPDATE inf SET  prijmeni= '". $prijmeni_n ."' WHERE jmeno = '" . $_SESSION['username'] . "'";
        if ($db -> query($update2) === TRUE)
        {
         echo('<script> alert ("Řádek byl upraven")</script>');
        }
        else
        {
         echo('<script> alert ("Řádek nebyl upraven")</script>'); 
        }
       }
       else if(isset($email_n))
       {
        $update3 = "UPDATE inf SET  email= '".$email_n."' WHERE jmeno = '" . $_SESSION['username'] . "'";
        if ($db -> query($update3) === TRUE)
        {
         echo('<script> alert ("Řádek byl upraven")</script>');
        }
        else
        {
         echo('<script> alert ("Řádek nebyl upraven")</script>'); 
        }
       }
       else if(isset($vek_n))
       {
        $update4 = "UPDATE inf SET  vek= '". $vek_n."' WHERE jmeno = '" . $_SESSION['username'] . "'";
        if ($db -> query($update4) === TRUE)
        {
         echo('<script> alert ("Řádek byl upraven")</script>');
        }
        else
        {
         echo('<script> alert ("Řádek nebyl upraven")</script>'); 
        }
       }
       else if(isset($datum_n))
       {
        $update5 = "UPDATE inf SET  datum= '". $datum_n ."' WHERE jmeno = '" . $_SESSION['username'] . "'";
        if ($db -> query($update5) === TRUE)
        {
         echo('<script> alert ("Řádek byl upraven")</script>');
        }
        else
        {
         echo('<script> alert ("Řádek nebyl upraven")</script>'); 
        }
       }
      ?>