select
    case
        when u.pay_method = '' then 'error'
        else u.pay_method
    end as pay_method,
    count(*) as num
from
    user_client_log u
    join product_info p on u.product_id = p.product_id
where
    p.product_name = 'anta'
    and step = 'select'
group by
    u.pay_method
order by
    num desc;

出题的是个语文水平不及格的货，做这种题纯属浪费时间