select
    pay_ability,
    concat(round(
        100.0*(sum(if (overdue_days is not NULL, 1, 0)) / count(*)),1
    ),'%') overdue_ratio
from
    loan_tb t1
    left join customer_tb t2 on t1.customer_id = t2.customer_id
group by
    pay_ability
order by overdue_ratio desc;