with t1 as (
select
ct.pay_ability pay_ability
,count(*) count
,sum(if(lt.overdue_days is not null, 1, 0)) num
from loan_tb lt 
inner join customer_tb ct
on lt.customer_id = ct.customer_id
group by ct.pay_ability) 
select 
pay_ability,
concat(round(num / count * 100, 1),'%')  overdue_ratio
from t1
order by overdue_ratio desc