SET SESSION group_concat_max_len = 1000000;
SELECT
rental_date AS meet_time,
store_id,
GROUP_CONCAT(CONCAT(UPPER(first_name), ' ', UPPER(last_name)) ORDER BY last_name, first_name SEPARATOR ', ') AS clients
FROM rental r
JOIN inventory i
ON i.inventory_id = r.inventory_id
JOIN customer c
ON c.customer_id = r.customer_id
group by rental_date, store_id