题解 | 商品销售排名

select
    product_name,
     convert(sum((succ_fail) * price), signed) as total
from
    (
        select
            ucl.product_id, 
            (
                case
                    when step="select" then 1
                    else 0
                end
            ) as succ_fail,
            price, 
            product_name
        from
            user_client_log as ucl
            inner join product_info as pi on ucl.product_id=pi.product_id
    ) as tmp
group by product_id
order by total desc
limit 2

注意

case
	when step="select" then 1
	else 0
end

神人题目说的不清不楚.....