list product

<!doctype html>
<head>
<title>product</title>
<style type="text/css">
span.row {
 display: table-row;
}
div.box {
 border:dashed 1px #eee;
 text-align:center;
 width:200px;
 height:50px;
 display: table-cell;
 padding:2px;
}
</style>
</head>
<body>
<?php
$id=isset($_GET['id'])?$_GET['id']:'';
$db=new mysqli('localhost', 'my_user', 'my_password', 'my_db');
if (mysqli_connect_error()) {
    die('Connect Error ('.mysqli_connect_errno().')'.mysqli_connect_error());
}
$qry="SELECT * FROM tbl_product".($id?" WHERE category_id='$id'":"");
if($data=$db->query($qry)){
  $i=1;
  echo "<span class=\"row\">\n";
  while ($obj = $data->fetch_object()) {
    echo ($i%3==0?"</span>\n<span>\n":"")
       ."<div class=\"box\"><img src=\"".$obj->product_image."\" alt=\"".$obj->product_title."\">"
       ."<br>".$obj->product_price
       ."</div>\n";
    $i++;
  }
  echo "</span>\n";
  $data->close();
}
$db->close();
?>
</body>
</html>