query

SELECT r.*, c.firstname, c.lastname, SUM(d.amount) AS amount FROM reservation r
INNER JOIN customer c ON c.id = r.customer_id
INNER JOIN reservation_details d ON d.reservation_id = r.id
GROUP BY d.reservation_id
ORDER BY r.id DESC


SELECT r . * , c . * , SUM( d.amount ) AS amount FROM reservation r
INNER JOIN customer c ON c.id = r.customer_id
INNER JOIN reservation_details d ON d.reservation_id = r.id
GROUP BY d.reservation_id
ORDER BY r.id DESC