How can I get a list of the most recent tags in a wordpress database?

I am not familiar with the wordpress schema at all and I need to get back a list, or array of the most recent tags from any post in the wordpress database.

I just need the data available on the home page so I can then manipulate it.

All the functions seem to be designed to work on a per-post basis.

开发者_C百科(Wordpress really makes me feel sorry for frequent wordpress programmers.)

This ain't pretty, maybe a MySQL junkie can optimize it a little;

SELECT $wpdb->terms.term_id, $wpdb->terms.name, $wpdb->terms.slug
FROM $wpdb->terms
    INNER JOIN $wpdb->term_taxonomy ON ($wpdb->terms.term_id = $wpdb->term_taxonomy.term_id)
    INNER JOIN $wpdb->term_relationships ON ($wpdb->terms.term_id = $wpdb->term_relationships.term_taxonomy_id)
    INNER JOIN $wpdb->posts ON ($wpdb->term_relationships.object_id = $wpdb->posts.ID)
WHERE $wpdb->term_taxonomy.taxonomy = 'post_tag'
ORDER BY $wpdb->posts.post_date DESC

This basically joins the term, term taxonomy, term relationship and post tables together, getting terms that are of the taxonomy 'post_tag', and currently have a relation with a post, then ordering them by the post's date, descending.

You might get the same term in the result set multiple times, but I can't work out how to use GROUP BY or HAVING to fix this, without messing up the date order.

So an example might in use might be;

$tags= $wpdb->get_results($query); // $query being the above SQL
foreach ($tags as $tag) {
    if (!isset($stack[$tag->term_id]))
        $stack[$tag->term_id] = $tag;
}
print_r($stack); // should print an array of all tags, ordered by last used

SELECT name, slug, tag_history.tagdate
FROM (SELECT wp_term_relationships.term_taxonomy_id AS tagid,
    substr(wp_posts.post_date_gmt,1,10) AS tagdate
    FROM wp_term_relationships 
    INNER JOIN wp_term_taxonomy ON wp_term_taxonomy.term_taxonomy_id=wp_term_relationships.term_taxonomy_id 
    INNER JOIN wp_posts ON wp_posts.ID=wp_term_relationships.object_id 
    WHERE taxonomy='post_tag' ORDER BY post_date_gmt DESC, wp_posts.post_title)
AS tag_history
INNER JOIN wp_terms ON wp_terms.term_id=tag_history.tagid
GROUP BY tag_history.tagid
ORDER BY tag_history.tagdate DESC

This is what I wrote as a workaround - sure it's possible to make it sharper! - to build a tag sitemap (XML, needing <LOC&> and <LASTMOD>...) based on the date of association tag<->post. You could add, at the end of the query, a LIMIT 0,10 to view only the 10 last associated tags.

This query will return three columns (name, slug and date of LAST association of single tag) you might use in many ways.

Remember that wp_ is the default dB prefix in WordPress. You have to change every occurrence with $wpdb-> (see TheDeadMedic's answer) and be sure to set $wpdb before the query.