Cette requête semble mieux mais je ne suis pas sûr que cela règlera le problème. Qu'en est-il ?
SELECT product_id AS `ID`, od.product_name AS `Nom du produit`, od.product_quantity AS `Qté` , DATE_FORMAT(tco.ordered_datetime, "%W %e %M %Y") AS `Date de la réservation`, DATEDIFF(tco.ordered_datetime, now() ) as `Dans x jour`, cu.firstname AS `Prénom`, cu.lastname AS `Nom`, cu.email, cu.id_default_group AS `Groupe : 3 Client, 4 Adhérent` FROM `ps_order_detail` od LEFT JOIN `ps_product` p ON p.id_product = od.product_id AND p.id_product != 1 LEFT JOIN `ps_terracalendar_order` tco ON (tco.id_product = p.id_product AND tco.id_order = od.id_order AND tco.ordered_datetime IS NOT NULL) LEFT JOIN `ps_orders` o ON o.id_order = tco.id_order LEFT JOIN `ps_customer` cu ON cu.id_customer = o.id_customer ORDER BY tco.ordered_datetime;