Display different sidebar based on category of single post

category-sidebar-in-single.php

<?php
if(is_single()) {
    $categories = new WPSEO_Primary_Term('category', get_the_ID());

    $category_id = $categories->get_primary_term();

    $category = &get_category($category_id);

    switch($category->slug) {
        case 'blog':
            continue;
        case 'thien-nguyen':
            smk_sidebar('sr461_252etf');
            break;
        case 'dau-tu-tai-chinh':
            smk_sidebar('sr461_138wel');
            break;
        default:
            dynamic_sidebar('sidebar-right');
            break;
    }

}
?>