LC 1484按日期分组销售产品Group Sold Products By The Date　简单

Activities 表记录每天售出的产品；按日期统计售出产品种数和产品名列表（去重、字典序、逗号分隔），按日期升序。

思路 COUNT(DISTINCT) + GROUP_CONCAT(DISTINCT ... ORDER BY)。

SELECT sell_date,
       COUNT(DISTINCT product) AS num_sold,
       GROUP_CONCAT(DISTINCT product
                    ORDER BY product) AS products
FROM Activities
GROUP BY sell_date
ORDER BY sell_date;

数据表：Activities　·　关键字：按日期统计售出产品种数和产品名列表（去重、字典序、逗号分隔），按日期升序