题解 | #某宝店铺折扣率#

SELECT ROUND(SUM(sales_price) / SUM(t_tag_price) * 100, 2) AS 'discount_rate(%)'
FROM (
    SELECT item_id, 
        sales_num * tag_price AS t_tag_price,
        sales_price 
    FROM sales_tb
        JOIN product_tb
        USING(item_id)
)total_price_t