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 a.merchant_id, 
        a.merchant_name, 
        b.total_sales_amount,
        c.total_refund_amount,
        d.average_satisfaction_score
FROM merchants_underline AS a
LEFT JOIN (
    SELECT merchant_id, SUM(sale_amount) AS total_sales_amount
    FROM sales_underline
    GROUP BY merchant_id
) AS b
ON a.merchant_id = b.merchant_id
LEFT JOIN (
    SELECT merchant_id, SUM(refund_amount) AS total_refund_amount
    FROM refunds_underline
    GROUP BY merchant_id
) AS c
ON b.merchant_id = c.merchant_id
LEFT JOIN (
    SELECT merchant_id, 
        ROUND(AVG(satisfaction_score), 2) AS average_satisfaction_score
    FROM satisfaction_underline
    GROUP BY merchant_id
) AS d
ON c.merchant_id = d.merchant_id
ORDER BY merchant_id;