単一のmysqlクエリで複数のリレーションテーブルから値を複数連結する方法

rel_destinationsで別の結合を使用する必要があります プラハを目的地としてオファーを取得します。これを元のクエリに参加させます。

SELECT offers.*, 
  GROUP_CONCAT(DISTINCT DEPC.name SEPARATOR ', ') AS depCities,
  GROUP_CONCAT(DISTINCT DESTC.name SEPARATOR ', ') AS destCities
FROM offers
INNER JOIN `rel_departments` ON (`rel_departments`.`offer_id` = `offers`.`id`)
INNER JOIN `departments` as DEPC ON (DEPC.`id` = `rel_departments`.`rel_id`)
INNER JOIN `rel_destinations` ON (`rel_destinations`.`offer_id` = `offers`.`id`)
INNER JOIN `destinations` as DESTC ON (DESTC.`id` = `rel_destinations`.`rel_id`)
INNER JOIN rel_destinations AS d1 ON d1.offer_id = offers.id
WHERE d1.rel_id = 1
GROUP BY offers.id

デモ