select top 7 item_name, item_reserve, count(bid_id) as bid_count, 
max(bid_amount) as highest_bid, 
item_reserve / max(bid_amount) * 100 as pct_increase
from vb_items
join vb_bids on item_id=bid_item_id
where item_sold = 0 
group by item_name, item_reserve
order by bid_count desc
item_reserve から maximum_bid までの増加率を知りたいです。これは多かれ少なかれ正しいと思いますが、数学は私の得意分野ではありません。