今天学习到了一个新的函数：group_concat

其使用方法：group_concat([distinct] 字段名 [order by 排序字段 asc/desc] [separator '分隔符'])

使用场景要求的输入输出如下：

输入：
Activities 表：
+------------+-------------+
| sell_date  | product     |
+------------+-------------+
| 2020-05-30 | Headphone   |
| 2020-06-01 | Pencil      |
| 2020-06-02 | Mask        |
| 2020-05-30 | Basketball  |
| 2020-06-01 | Bible       |
| 2020-06-02 | Mask        |
| 2020-05-30 | T-Shirt     |
+------------+-------------+
输出：
+------------+----------+------------------------------+
| sell_date  | num_sold | products                     |
+------------+----------+------------------------------+
| 2020-05-30 | 3        | Basketball,Headphone,T-shirt |
| 2020-06-01 | 2        | Bible,Pencil                 |
| 2020-06-02 | 1        | Mask                         |
+------------+----------+------------------------------+

也就是先根据sell_date进行分组group by，根据分组的结果对products进行group_concat，并设置排序方式和间隔符号

给出解决以上场景的sql代码：

select sell_date,count(distinct product) as num_sold,
group_concat(distinct product order by product asc separator "," ) as products 
from Activities
group by sell_date