with a as(
    select product_id,
        count(*) as buy_count
    from user_client_log
    where step='order'
    group by product_id
),
b as (
    select
        max(buy_count) as max_count
    from a
)
select product_id,buy_count as cnt
from a join b
where buy_count=max_count
order by cnt desc,product_id