在开发wordpress主题的过程中，我们可能会有这样的需求，既然可以获取某个分类的关联标签，那么，我们能获取某个标签的关联分类吗？答案是肯定的。以下提供一个获取同一标签下的关联分类的函数：

function ludou_get_tag_categories($args) {
global $wpdb;
$categories = $wpdb->get_results
("
SELECT DISTINCT terms1.term_id as cat_id
FROM
$wpdb->posts as p1
LEFT JOIN $wpdb->term_relationships as r1 ON p1.ID = r1.object_ID
LEFT JOIN $wpdb->term_taxonomy as t1 ON r1.term_taxonomy_id = t1.term_taxonomy_id
LEFT JOIN $wpdb->terms as terms1 ON t1.term_id = terms1.term_id,
$wpdb->posts as p2
LEFT JOIN $wpdb->term_relationships as r2 ON p2.ID = r2.object_ID
LEFT JOIN $wpdb->term_taxonomy as t2 ON r2.term_taxonomy_id = t2.term_taxonomy_id
LEFT JOIN $wpdb->terms as terms2 ON t2.term_id = terms2.term_id
WHERE
t1.taxonomy = 'category' AND p1.post_status = 'publish' AND terms2.term_id IN (".$args['tags'].") AND
t2.taxonomy = 'post_tag' AND p2.post_status = 'publish'
AND p1.ID = p2.ID
ORDER by cat_id
");
$count = 0;

if($categories) {
foreach ($categories as $category) {
$mycategory[$count] = get_term_by('id', $category->cat_id, 'category');
$count++;
}
}
else {
$mycategory = NULL;
}

return $mycategory;
}

下面是一个简单的函数调用范例：

$args = array( 'tags' => '12,13');// 定义一个tag数据，存放多个tagID，12,13是标签ID，多个用英文逗号隔开
$categories = ludou_get_tag_categories($args);// 调用上面定义的函数，来获取ID为12，13的标签的关联分类
// 输出我们获取到的关联分类，以列表形式打印
$content .= "<ul>";
if(!empty($categories)) {
foreach ($categories as $category) {
$content .= "<li><a href=\"".get_category_link( $category->term_id )."\">".$category->name."</a></li>";
}
}
$content .= "</ul>";
echo $content;

通过上面的代码，我们在wordpress主题中实现了调用同一标签下的关联分类，并列举了一个简单案例，当然，你还可以更加深入一点。