bagaimana cara select post berdasarkan tag dengan php..?

gan gimana cara menapilkan post berdasarkan tag di php..? ane udah buat gini scriptnya.. tapi error mysql_fetch_array() expects parameter 1 to be resource, boolean given in C:\xampp\htdocs\blog\konten.php on line 11

<?php
	if(!defined("INDEX")) die("---");

	$hal 	= isset($_GET['hal']) ? $_GET['hal'] : 1;

	$batas	= 20;
	$posisi = ($hal-1) * $batas ;
	$tag = 'html';
	$artikel = mysql_query("SELECT tag from artikel WHERE tag=$tag desc limit $posisi, $batas");
	while($data=mysql_fetch_array($artikel)){
?>
	<div class="col-xs-12 col-sm-4 col-md-3 homewrap">
			<?php if($data['gambar']!="") ?> <img src="gambar/artikel/<?php echo $data['gambar']; ?>">
			<div class="clashover">
			<h4 class="judul"><?php echo $data['judul']; ?></h4>
			<h5><a href="../<?php echo $data['demo'] ;?>" target="_blank"><span class="glyphicon glyphicon-play"></span> Demo</a></h5>
			<h5><a href="../<?php echo $data['download']; ?>" target="_blank"><span class="glyphicon glyphicon-save"></span> Download</a></h5>
			</div>
		</div>

<?php
	}
; ?>
<div class="clearfix">

</div>