in that case, i would create an array so it can be re-used. it can be keyed by category_id so you know which category you are accessing.
PHP Code:
<?
$result = mysql_query("select c.category_id, c.category_name, count(a.article_id) as count from np_categories as c
left join np_articles as a on c.category_id=a.article_category_id
group by c.category_id
order by c.category_name");
while ($row = mysql_fetch_assoc($result)) {
$categories[$row['category_id']] = $row;
}
// now echo the name and article count of category id 15
echo $categories[15]['category_name'] . " (" . $categories[15]['count'] . ")";
?>