Wordpress - Cross Taxonomy Tag List Query

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<?php
/**
 Echo a list of tags terms for posts that are also have a $where_tax of $where_slug
 Queries added to transient cache for performance
 Note: Using the slug for a Taxonomy in $where_slug for simpler query
 Tested up to WP 3.3, drop it in your functions.php

Example: Get a tag list for Posts in the 'News' Category
 tags_by_other_taxonomy('news');

Example: Get a tag list for Bands (custom post type) in the 'Rock' Genre (custom taxonomy)
 tags_by_other_taxonomy('rock','genre','band');
*/

function tags_by_other_taxonomy($where_slug,$where_tax = 'category',$post_type = 'post',$bust_cache = false) {
    $cache_key = "{$where_slug}:{$where_tax}";
    $cache = get_transient('sc_cross_tax');
    if ( true !== $bust_cache and false !== $cache and isset($cache[$cache_key]) and !empty($cache[$cache_key]) ) {
            echo '<!-- cache -->',$cache[$cache_key];
    } else {
        global $wpdb;
        $cat_id = $wpdb->get_var("SELECT tt.term_taxonomy_id FROM $wpdb->terms t INNER JOIN $wpdb->term_taxonomy tt ON t.term_id = tt.term_id WHERE t.slug = '{$where_slug}' AND tt.taxonomy = '{$where_tax}' LIMIT 1");
        if( !empty($cat_id) ) {
            $cat_posts = $wpdb->get_col("SELECT tr.object_id FROM $wpdb->term_relationships tr inner join $wpdb->posts p ON p.ID = tr.object_id WHERE term_taxonomy_id = {$cat_id} AND p.post_status = 'publish' AND p.post_type = '{$post_type}'");
            if( count($cat_posts) )
                $tags = $wpdb->get_results("SELECT DISTINCT t.name,t.slug FROM $wpdb->term_taxonomy tt
                                INNER JOIN $wpdb->term_relationships tr ON tt.term_taxonomy_id = tr.term_taxonomy_id
                                INNER JOIN $wpdb->terms t ON t.term_id = tt.term_id
                                WHERE tt.taxonomy = 'post_tag' and tr.object_id IN (".implode(',',$cat_posts) .')');
                $html = '<ul class="post-tags-'.$where_slug.'">';
                if( count($tags) ) {
                    foreach($tags as $tag) {
                        $html .= '<li><a href="/tag/'.$tag->slug.'/" title="Posts tagged with '.$tag->name.'">'.$tag->name.'</a></li>';
                    }
                }
                $html .= '</ul>';

                if( !is_array($cache) )
                    $cache = array();
                $cache[$cache_key] = $html;
                set_transient('sc_cross_tax', $cache, 86400);
                echo '<!-- no cache -->',$html;
        }
    }
}