CRUD Simple

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
<style type="text/css">
<!--
#form1 table tr td {
    text-align: center;
}
-->
</style>
</head>
<?PHP

include('koneksi.php');

//SCRIPT untuk save dan simpan baru
    if($_POST){
        $id       = $_POST['id'] ;
        $username = $_POST['username'];
        $password = $_POST['password'];
        if (empty($username) || empty($password)){

            echo"Username atau Password tidak boleh kosong";

        }else{

            //untuk ngecek kalo variabel idnya ada perintah sql yang di jalannin sql untuk edit kalo variabel idnya kosong perintah yang di jalanin sql untuk save
            if(!empty($id)){
                $simpan = mysql_query("UPDATE  user SET  username =  '$username', password =  '$password' WHERE  id = '$id';");
            }else{
                $simpan = mysql_query("INSERT INTO user (`id`, `username`, `password`) VALUES ('NULL', '$username', '$password')");
            }

            if($simpan){
                echo"<script>alert('Data tersimpan!');document.location.href='login.php';</script>";
            }
            else{
                echo"<script>alert('Data gagal tersimpan!');document.location.href='login.php';</script>";
            }

        }

    }
//Kalo get edit, mengambil data dan sebagainya dari database
    if(isset($_GET['edit'])){
        $sql = "SELECT * FROM  user WHERE id = '$_GET[id]'";
        $query = mysql_query($sql);
        $r = mysql_fetch_array($query);
    }
//SCRIPT HAPUS
    if(isset($_GET['hapus'])){
        $hapus = mysql_query("DELETE FROM user where id = '$_GET[id]'");
        if($hapus){
            echo"Data Terhapus!";
        }
        else{
            echo"Data Gagal Terhapus!";
        }
    }


?>


<body>
<form id="form1" name="form1" method="post" action="">
    <input type="hidden" name="id" value="<?php echo (isset($r))? $r['id'] : '';?>">
  <table width="270" border="0" cellspacing="1" cellpadding="2">
    <tr>
      <td colspan="2">FORM USER</td>
    </tr>
    <tr>
      <td width="96">Username</td>
      <td width="163"><label>
        <input type="text" name="username" id="textfield"  value="<?php echo (isset($r))? $r['username'] : '';?>"/>
      </label></td>
    </tr>
    <tr>
      <td>Password</td>
      <td><label>
        <input type="text" name="password" id="textfield2"  value="<?php echo (isset($r))? $r['password'] : '';?>"/>
      </label></td>
    </tr>
    <tr>
      <td colspan="2"><label>
        <input type="submit" name="button" id="button" value="Submit" />
        <input type="reset" name="button2" id="button2" value="Cancel" />
      </label></td>
    </tr>
  </table>
</form>
<table>
    <tr>
        <td>No</td>
        <td>Usenname</td>
        <td>Password</td>
    </tr>
    <?php
        $sql = "SELECT * FROM user ";
        $query = mysql_query($sql);
        $no = 0;
        while($row = mysql_fetch_array($query)){
            $no++;
    ?>
    <tr>
        <td><?php echo $no; ?></td>
        <td><?php echo $row['1'];?></td>
        <td><?php echo $row['password']; ?></td>
        <td><a href="?edit&id=<?php echo $row['id']; ?>">Edit</a> | <a href="?hapus&id=<?php echo $row['id']; ?>">Delete</a></td>
    </tr>
    <?php
        }
    ?>
</table>


</body>
</html>