select count(*) from ec_subcategories where subcategory_id=:subcategory_id and sort_key=:sort_key
select count(*) from ec_subcategories where subcategory_id=:next_subcategory_id and sort_key=:next_sort_key
update ec_subcategories set sort_key=:next_sort_key where subcategory_id=:subcategory_id
update ec_subcategories set sort_key=:sort_key where subcategory_id=:next_subcategory_id