I needed to list all the categories of a custom post type that an author had posted in.
I found code to do that with regular posts in the wordpress.org forums and I modified it to use with custom post types.
Be sure to replace custom_taxonomy with the name of your taxonomy.
Place this into your theme file where you want the list to appear.
<?php $author = get_the_author_meta('ID'); $categories = $wpdb->get_results(" SELECT DISTINCT(terms.term_id) as ID, terms.name, terms.slug FROM $wpdb->posts as posts LEFT JOIN $wpdb->term_relationships as relationships ON posts.ID = relationships.object_ID LEFT JOIN $wpdb->term_taxonomy as tax ON relationships.term_taxonomy_id = tax.term_taxonomy_id LEFT JOIN $wpdb->terms as terms ON tax.term_id = terms.term_id WHERE 1=1 AND ( posts.post_status = 'publish' AND posts.post_author = '$author' AND tax.taxonomy = 'custom_taxonomy' ) ORDER BY terms.name ASC "); ?> <ul> <?php foreach( $categories as $category ) : ?> <li> <a href="<?php echo get_term_link( $category->name, 'custom_taxonomy' ); ?>" title="<?php echo $category->name ?>"><?php echo $category->name ?></a> </li> <?php endforeach; ?> </ul>