题解 | 查询出每个品牌在不同月份的总销售额以及购买该品牌商品的用户的平均年龄

SELECT
    category_id,
    round(sum(order_amount), 2) total_sales,
    sum(
        CASE
            WHEN customer_gender = '男' THEN 1
            ELSE 0
        END
    ) male_customers,
    sum(
        CASE
            WHEN customer_gender = '女' THEN 1
            ELSE 0
        END
    ) female_customers
FROM
    (
        SELECT
            a.category_id,
            a.order_amount,
            b.customer_gender
        FROM
            order_details AS a
            INNER JOIN customer_info AS b ON a.order_id = b.order_id
        WHERE
            a.order_date BETWEEN '2024-01-01' AND '2024-06-30'
    ) AS t
GROUP BY
    category_id
ORDER BY
    category_id ASC

此题ez，先将给的两个表连结取出来需要用的数据，然后再GROUP BY 聚合就好了