SQL练习三—用户分级占比

问题分析：

1.表连接 

2.占比：逾期 overdue_days不是null/全部   count() 会忽略null值，count(*)会计数所有行

count(overdue_days)/count(distinct customer_id)

3.输出百分比：concat(round(count()/count()*100,1),'%')   

4.输出条件：order by overdue_ratio desc

易错点：多表连接时，给字段名加上表名前缀

select
pay_ability,
concat(round(count(overdue_days)/count( distinct c.customer_id)*100,1),'%') as
overdue_ratio
from customer_tb as c
left join loan_tb as l
on c.customer_id=l.customer_id
group by pay_ability
order by overdue_ratio desc;