Chyba v update dotazu

<form method="POST"  action="inf.php" class="form">
     <br />
     <br />
     <table>
      <tr>
       <td colspan="2" align="center">Vyplň pole která chceš upravit</td>
      </tr>
      <tr>
       <td>Tvé uživatelké jméno: </td>
       <td><?php echo( $_SESSION['username'])?></td>
      </tr>
      <tr>
       <td>Jméno:</td>
       <td><input type="text"  name="jmeno_u" placeholder="Zadej své jméno" /></td>
      </tr>
      <tr>
       <td>Příjmení:</td>
       <td><input type="text"  name="prijmeni_u" placeholder="Zadej své příjmení" /></td>
      </tr>
      <tr>
       <td>Bydliště:</td>
       <td><input type="text"  name="bydliste_u" placeholder="Zadej své bydliště" /></td>
      </tr>
      <tr>
       <td>Číslo popisné:</td>
       <td><input type="number"  name="cislo_domu_u" placeholder="Zadej číslo domu" /></td>
      </tr>
      <tr>
       <td>Pošta:</td>
       <td><input type="text"  name="posta_u" placeholder="Zadej název pošty" /></td>
      </tr>
      <tr>
       <td>PSČ:</td>
       <td><input type="number"  name="psc_u"  placeholder="Zadej PSČ" /></td>
      </tr>
      <tr>
       <td>Datum narození:</td>
       <td><input type="date"  name="datum_u" /></td>
      </tr>      
      <tr>
       <td>Věk:</td>
       <td><input type="number"  name="vek_u" placeholder="Zadej svůj věk" /></td>
      </tr>
      <tr>
       <td>E-mail:</td>
       <td><input type="text"  name="email_u" placeholder="Zadej svůj e-mail" /></td>
      </tr>
      <tr>
       <td>Telefon:</td>
       <td><input type="number"  name="telefon_u" placeholder="Zadej svůj telefon" /></td>
      </tr>
       <td>&nbsp;</td>
       <td ><center><input type="submit" value="Uprav záznam" class="button" ></center></td>
      </tr>
    </form>
    <?php
      $jmeno_u = $_POST["jmeno_u"];
      $prijmeni_u = $_POST["prijmeni_u"];
      $bydliste_u = $_POST["bydliste_u"];
      $cislo_domu_u = $_POST["cislo_domu_u"];
      $posta_u = $_POST["posta_u"];
      $psc_u = $_POST["psc_u"];
      $datum_u = $_POST["datum_u"];
      $vek_u = $_POST["vek_u"];
      $email_u = $_POST["email_u"];
      $telefon_u = $_POST["telefon_u"];
      $sets_u = array();
      
       if (isset($_POST['jmeno_u']) && strlen(trim($_POST['jmeno_u']))) 
       {
        $sets[] = "jmeno = '" . trim($_POST['jmeno_u']) . "'";
       }
  
       if (isset($_POST['prijmeni_u']) && strlen(trim($_POST['prijmeni_u']))) 
       {
        $sets[] = "prijmeni = '" . trim($_POST['prijmeni_u']) . "'";
       }
  
        if (isset($_POST['bydliste_u']) && strlen(trim($_POST['bydliste_u']))) 
        {
         $sets[] = "bydliste = '" . trim($_POST['bydliste_u']) . "'"; 
        }
  
        if (isset($_POST['cislo_domu_u']) && strlen(trim($_POST['cislo_domu_u']))) 
        {
         $sets[] = "cislo_domu = " . intval(trim($_POST['cislo_domu_u']));
        }
  
        if (isset($_POST['posta_u']) && strlen(trim($_POST['posta_u']))) 
        {
         $sets[] = "posta = '" . trim($_POST['posta_u']) . "'";
        }

        if (isset($_POST['psc_u']) && strlen(trim($_POST['psc_u']))) 
        {
         $sets[] = "psc = '" . trim($_POST['psc_u']) . "'";
        }
        
        if (isset($_POST['datum_u']) && strlen(trim($_POST['datum_u']))) 
        {
         $sets[] = "datum = '" . trim($_POST['datum_u']) . "'";
        }

        if (isset($_POST['vek_u']) && strlen(trim($_POST['vek_u']))) 
        {
         $sets[] = "vek = '" . trim($_POST['vek_u']) . "'";
        }

        if (isset($_POST['email_u']) && strlen(trim($_POST['email_u']))) 
        {
         $sets[] = "email = '" . trim($_POST['email_u']) . "'";
        }

        if (isset($_POST['telefon_u']) && strlen(trim($_POST['telefon_u']))) 
        {
         $sets[] = "telefon = '" . trim($_POST['telefon_u']) . "'";
        }
        if(count($sets) == 1) 
        {
         $update = "UPDATE registrace SET " . implode(', ', $sets) . " WHERE jmeno = '" . $_SESSION['username'] . "'";
         if ($db->query($update) == TRUE)
         {
          echo("<script>alert('Záznam byl upraven')</script>");
         } 
         else 
         {
          echo("<script>alert('Záznam nebyl upraven')</script>");
         }
        }
      ?>