SELECT t2.pay_ability,
       CONCAT(ROUND(SUM(CASE WHEN t1.overdue_days IS NOT NULL THEN 1 ELSE 0 END)/COUNT(*)*100,1),'%') AS overdue_ratio
FROM loan_tb t1
LEFT JOIN customer_tb t2 ON t1.customer_id=t2.customer_id
GROUP BY t2.pay_ability
ORDER BY overdue_ratio DESC