$result = mysql_query("SELECT catID FROM blah ORDER BY catID DESC");
$row = mysql_fetch_array($result);

/* Process all the items in each category */
for ($i=1; $i<=$row['catID']; $i++) {
	$result = mysql_query("SELECT * from blah WHERE catID=".$i."");
	$row = mysql_fetch_array($result);

	/* Work with row here */
}