Get all tags based on specific category (including all tags from child categories and posts) wordpress

Question

I wanted to use wp_tag_cloud() on single.php using the argument that gets all tags from specific category including all tags from its child categories and posts.

Answer 1

In your theme's functions.php insert the following function:

function get_category_tags($args) {
    global $wpdb;
    $tags = $wpdb->get_results
    ("
        SELECT DISTINCT terms2.term_id as tag_id, terms2.name as tag_name, null as tag_link
        FROM
            wp_posts as p1
            LEFT JOIN wp_term_relationships as r1 ON p1.ID = r1.object_ID
            LEFT JOIN wp_term_taxonomy as t1 ON r1.term_taxonomy_id = t1.term_taxonomy_id
            LEFT JOIN wp_terms as terms1 ON t1.term_id = terms1.term_id,

            wp_posts as p2
            LEFT JOIN wp_term_relationships as r2 ON p2.ID = r2.object_ID
            LEFT JOIN wp_term_taxonomy as t2 ON r2.term_taxonomy_id = t2.term_taxonomy_id
            LEFT JOIN wp_terms as terms2 ON t2.term_id = terms2.term_id
        WHERE
            t1.taxonomy = 'category' AND p1.post_status = 'publish' AND terms1.term_id IN (".$args['categories'].") AND
            t2.taxonomy = 'post_tag' AND p2.post_status = 'publish'
            AND p1.ID = p2.ID
        ORDER by tag_name
    ");
    $count = 0;
    foreach ($tags as $tag) {
        $tags[$count]->tag_link = get_tag_link($tag->tag_id);
        $count++;
    }
    return $tags;
}

In your theme document call the function as follows. Notice it accepts multiple category id's:

 $args = array(
        'categories'                => '12,13,14'
    );

$tags = get_category_tags($args);

This will return an array that you could do the following with:

$content .= "
";
foreach ($tags as $tag) {
    $content .= "
tag_link\">$tag->tag_name
";
}
$content .= "
";
echo $content;