select  
c.pay_ability,

concat( FORMAT(sum(case when coalesce(overdue_days,0)>0  then 1 else 0 end) /count(1)*100,1),'%')  as overdue_ratio



from 
loan_tb as l 
 join customer_tb as c 
on l.customer_id=c.customer_id


group by 
c.pay_ability

order by 2 desc