题解 | 电商平台需要对商家的销售业绩、退款情况和客户满意度进行综合评估

select merchant_id,merchant_name,total_sales_amount,total_refund_amount,average_satisfaction_score
from 
 (select merchant_id,sum(sale_amount) as total_sales_amount
from sales_underline
group by merchant_id) a
join 
 (select merchant_id,sum(refund_amount) as total_refund_amount
from refunds_underline
group by merchant_id) b 
using(merchant_id)
join merchants_underline
using(merchant_id)
join 
(
    select merchant_id,round(avg(satisfaction_score),2) as average_satisfaction_score
    from satisfaction_underline
    group by merchant_id
) c
using(merchant_id)