Mysql左连接表2，其中来自表3的字段

表媒体

id, options
1   a
2   b
3   c

表格地图

id, title, type
1   f      x
2   g      x    
3   h      y    
4   z      x
4   w      y

表媒体地图

maps_id  media_id   
1        2
2        3

我正在尝试从表介质中选择所有数据并连接表映射。每个媒体可以包含多个地图

SELECT media_t.id, media_t.options,
    GROUP_CONCAT(CASE WHEN maps_t.type = 'x' THEN maps_t.title END ORDER BY maps_t.title SEPARATOR ', ') as x,
    GROUP_CONCAT(CASE WHEN maps_t.type = 'y' THEN maps_t.title END ORDER BY maps_t.title SEPARATOR ', ') as y
    FROM media_table as media_t
    LEFT JOIN maps_table as maps_t
    ON media_t.id = (
        SELECT maps_id FROM {table_media_maps} 
        WHERE media_id = maps_t.id
    )
    GROUP BY media_t.id

---

如果你需要加入3个tbals，你可以试试

SELECT me.id, me.options,
GROUP_CONCAT(CASE WHEN ma.type = 'x' THEN ma.title END ORDER BY ma.title SEPARATOR ', ') as x,
GROUP_CONCAT(CASE WHEN ma.type = 'y' THEN ma.title END ORDER BY ma.title SEPARATOR ', ') as y
FROM media as me
LEFT JOIN media_maps mm on me-id = mm.media_id 
LEFT JOIN maps  ma  ON mm.maps_id = ma.id
GROUP BY me.id

---

无论如何，您的数据都不是完整的。 我为maps表设置了一个右连接，这样您就可以看到它是有效的，很可能您希望还有一个左连接，但是您仍然需要连接所有三个表

---

DBFIDLE

您的解决方案和scaisEdge解决方案有什么区别？他的解决方案不会显示第一行，因为右连接获取所有数据并尝试将其与其余数据连接起来，elsw这与你所看到的解决方案相同，只是观察到右连接非常罕见，但我不介意，当我测试我的查询时，我发现数据不完整，并且根本没有显示组连接，所以我构建了它，只是为了看看，但我提到他可能想要左连接

CREATE TABLE media_table  (
  `id` INTEGER,
  `options` VARCHAR(1)
);

INSERT INTO media_table 
  (`id`, `options`)
VALUES
  ('1', 'a'),
  ('2', 'b'),
  ('3', 'c');

CREATE TABLE table_media_maps (
  `maps_id` INTEGER,
  `media_id` INTEGER
);

INSERT INTO table_media_maps
  (`maps_id`, `media_id`)
VALUES
  ('1', '2'),
  ('2', '3');

CREATE TABLE maps_table  (
  `id` INTEGER,
  `title` VARCHAR(1),
  `type` VARCHAR(1)
);

INSERT INTO maps_table 
  (`id`, `title`, `type`)
VALUES
  ('1', 'f', 'x'),
  ('2', 'g', 'x'),
  ('3', 'h', 'y'),
  ('4', 'z', 'x'),
  ('4', 'w', 'y');

SELECT media_t.id, media_t.options,
    GROUP_CONCAT(
    CASE WHEN maps_t.type = 'x' THEN maps_t.title END
    ORDER BY maps_t.title SEPARATOR ', ') 
    as x,
    GROUP_CONCAT(
    CASE WHEN maps_t.type = 'y' THEN maps_t.title END
    ORDER BY maps_t.title SEPARATOR ', ') 
    as y
    FROM media_table as media_t
    LEFT JOIN table_media_maps m_m_t ON media_t.id = m_m_t.media_id
    right JOIN maps_table as maps_t
    ON maps_t.id = m_m_t.maps_id
    GROUP BY media_t.id, media_t.options

id | options | x | y ---: | :------ | :- | :--- null | null | z | h, w 2 | b | f | null 3 | c | g | null