select
    t.pay_ability,
    concat(round(sum(t.customer_type)*100.0/count(t.customer_id),1),"%") as overdue_ratio
from
    (select
        distinct 
        lt.customer_id,
        ct.pay_ability,
        case when lt.overdue_days is not null then 1 else 0 end as customer_type
    from
        loan_tb lt
    left join
        customer_tb ct on lt.customer_id = ct.customer_id) t
group by 
    1
order by 
    2 desc