# 문제
https://leetcode.com/problems/group-sold-products-by-the-date/description/
# 문제 설명

# 핵심 개념
그룹별로 컬럼의 값을 , 로 합쳐주는 함수
group_concat( 합칠값 )
# 정답 코드
select date_format(sell_date, '%Y-%m-%d') as sell_date,
count(distinct product) as num_sold,
group_concat(distinct product) as products
from Activities
group by sell_date