How do categories and subcategories for WooCommerce are saved in DB?
function getParentCategories() { global $wpdb; $sql = "SELECT term_id as id, name, slug FROM wp_terms where term_id in (SELECT term_id FROM wp_term_taxonomy where parent = 0 and taxonomy = 'category') order by name asc"; $parents = $wpdb->get_results( $sql ); return $parents;}function getChildCategories($id) { global $wpdb; $sql = "SELECT term_id as id, name, slug FROM wp_terms where term_id in (SELECT term_id FROM wp_term_taxonomy where parent = $id and taxonomy = 'category') order by name asc"; $children = $wpdb->get_results( $sql ); return $children;}
You have to look into table wp_options for option_name "product_cat_children", there is serialized category hierarchy.
Maybe because one is the parent and the other the child, so if you define this relation, it's right that the opposite shouldn't work.