$from = "vw_products_allclass AS T1"
. " JOIN ("
. " SELECT max(T3.rank) AS category_rank,"
. " max(T2.rank) AS product_rank,"
. " T2.product_id"
. " FROM dtb_product_categories T2"
. " JOIN dtb_category T3 USING (category_id)"
. " GROUP BY product_id) AS T4 USING (product_id)";
$order = "T4.category_rank DESC, T4.product_rank DESC";

A-+-B
+-C
+-D
のような階層のカテゴリ分類の場合、B,C,Dのランクは指定できますがAのランクは管理画面で指定できません。

B,C,Dの場合は、カテゴリが特定できるのでいいのですが、Aの一覧を表示する場合は、B,C,Dすべての商品の対象になるのでどのような順番に表示したらよいのでしょうか？

Aの分類でのランク登録を可能にするのがスマートのような気がしますが、変更箇所が多くなりそうで．．．

一つの商品をB,C,Dに登録可能なので、一つの商品で複数のランクがあることになります。
カテゴリ・ランク＋商品・ランクをキーにして、同一商品の場合は、カテゴリ・ランクが小さい方を優先させればいいのかな？

default:
$col = "DISTINCT T1.product_id, product_code_min, product_code_max,"
. " price01_min, price01_max, price02_min, price02_max,"
. " stock_min, stock_max, stock_unlimited_min,"
. " stock_unlimited_max, del_flg, status, name, comment1,"
. " comment2, comment3, main_list_comment, main_image,"
. " main_list_image, product_flag, deliv_date_id, sale_limit,"
. " point_rate, sale_unlimited, create_date, deliv_fee, "
. " T4.product_rank, T4.category_rank";
$from = "vw_products_allclass AS T1"
. " JOIN ("
. " SELECT max(T3.rank) AS category_rank,"
. " max(T2.rank) AS product_rank,"
. " T2.product_id"
. " FROM dtb_product_categories T2"
. " JOIN dtb_category T3 USING (category_id)"
. " GROUP BY product_id) AS T4 USING (product_id)";
$order = "T4.category_rank DESC, T4.product_rank DESC";
break;

default:
$col = "product_id, product_code_min, product_code_max,"
. " price01_min, price01_max, price02_min, price02_max,"
. " stock_min, stock_max, stock_unlimited_min,"
. " stock_unlimited_max, del_flg, status, name, comment1,"
. " comment2, comment3, main_list_comment, main_image,"
. " main_list_image, product_flag, deliv_date_id, sale_limit,"
. " point_rate, sale_unlimited, create_date, deliv_fee, "
. " max(category_rank) AS category_rank, rank AS product_rank";
$from = "vw_products_allclass as TA1";
$order = "category_rank DESC, product_rank DESC";
$objQuery->setgroupby(product_id);
break;

$objQuery->setgroupby(product_id);