SET SESSION group_concat_max_len = 1000000;
select
r.rental_date as meet_time,
s.store_id,
group_concat(distinct concat(c.first_name, ' ', c.last_name)order by c.last_name, c.first_name separator ',') as customers
from customer as c
join rental as r on c.customer_id = r.customer_id
join staff as s on r.staff_id = s.staff_id
group by r.rental_date, s.store_id
having count (*) >1
order by meet_time, s.store_id