我遇到了一些问题，围绕着多对多的查询。我有以下表格：
mysql> desc tags;
+------------+------------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+------------------+------+-----+---------------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| created_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| updated_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| user_id | bigint(20) | NO | | NULL | |
| name | varchar(64) | NO | | NULL | |
+------------+------------------+------+-----+---------------------+----------------+
mysql> desc response_and_tag_relationships;
+-------------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------+------------------+------+-----+---------+-------+
| response_id | int(10) unsigned | NO | PRI | NULL | |
| tag_id | int(10) unsigned | NO | PRI | NULL | |
+-------------+------------------+------+-----+---------+-------+
mysql> desc survey_responses;
+--------------+------------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| created_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| updated_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| survey_id | bigint(20) | NO | | NULL | |
| response | text | NO | | NULL | |
| score | smallint(6) | NO | | NULL | |
| recipient_id | bigint(20) | NO | | NULL | |
+--------------+------------------+------+-----+---------------------+----------------+
mysql> desc surveys;
+--------------+------------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------------+------+-----+---------------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| created_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| updated_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| survey_token | varchar(255) | NO | | NULL | |
| type | smallint(6) | NO | | NULL | |
| name | varchar(255) | NO | | NULL | |
+--------------+------------------+------+-----+---------------------+----------------+
mysql> desc people;
+------------+------------------+------+-----+---------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+------------------+------+-----+---------------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| created_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| updated_at | timestamp | NO | | 0000-00-00 00:00:00 | |
| email | varchar(255) | NO | | NULL | |
| last_sent | datetime | NO | | NULL | |
| name | varchar(255) | NO | | NULL | |
| dob | date | NO | | NULL | |
+------------+------------------+------+-----+---------------------+----------------+
我需要对响应中的标签进行分组。所以我想出了以下SQL（我的知识有限），这似乎可以完成这项工作：
SELECT
rat.tag_id,
rat.response_id,
t.name,
sr.response,
p.name,
p.email
FROM
response_and_tag_relationships rat
INNER JOIN tags t ON t.id=rat.tag_id
INNER JOIN survey_responses sr ON sr.id=rat.response_id
INNER JOIN surveys s ON s.id = sr.survey_id
INNER JOIN people p ON p.id=sr.recipient_id
WHERE
t.name IN (SELECT name FROM tags);
并产生以下结果：
+--------+-------------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------+-----------------------------------+
| tag_id | response_id | name | response | name | email |
+--------+-------------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------+-----------------------------------+
| 1 | 1 | ex | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 3 | 1 | repudiandae | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 4 | 1 | nam | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 5 | 1 | excepturi | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 6 | 1 | quasi | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 7 | 1 | perferendis | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 8 | 1 | nisi | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
| 9 | 1 | sint | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
但我认为我的逻辑向后，因为这是响应驱动，而不是标记驱动（我认为......）。我基本上只需要一个匹配结果的标签列表，以便在响应调用api方法中返回 - 那么有更好的方法吗？
修改
我理想的结果是（虽然我不相信它可能）：
+--------+-------------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------+-----------------------------------+
| tag_id | response_id | name | response | name | email |
+--------+-------------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------+-----------------------------------+
| 1,3,4,5,6,7,8,9 | 1 | ex | Repudiandae nam excepturi quasi perferendis nisi sint. Et excepturi id facere modi et sed. Eius nihil repellat veritatis voluptas. | Miss Sally Breitenberg | kkiehn@breitenberg.net |
我还需要在Laravel eloquent orm中构建这个，但我猜测只是一个原始查询是最好的
答案 0 :(得分：1)
从预期的结果集中确定它更像是您尝试对标记ID进行分组，是的，您可以使用group_concat函数作为
SELECT
group_concat(rat.tag_id) as tag_ids,
rat.response_id,
t.name,
sr.response,
p.name,
p.email
FROM
response_and_tag_relationships rat
INNER JOIN tags t ON t.id=rat.tag_id
INNER JOIN survey_responses sr ON sr.id=rat.response_id
INNER JOIN surveys s ON s.id = sr.survey_id
INNER JOIN people p ON p.id=sr.recipient_id
group by rat.response_id
现在，针对每个不同response_id的上述查询会将tag_id分组为逗号分隔字符串。
另请注意，使用group by并从多对多中选择数据时可能会返回任意值，例如，如果我们在选择中保留t.name，那么它可能是多对多关系中的任何一个在进行连接之后，对其他值进行连接。
理想情况下，您不应该在这些情况下选择这些列，或者在group_concat之类的聚合函数中使用它们。理想的查询是
SELECT
group_concat(rat.tag_id) as tag_ids,
rat.response_id
FROM
response_and_tag_relationships rat
INNER JOIN tags t ON t.id=rat.tag_id
INNER JOIN survey_responses sr ON sr.id=rat.response_id
INNER JOIN surveys s ON s.id = sr.survey_id
INNER JOIN people p ON p.id=sr.recipient_id
group by rat.response_id
如果您在select中也需要其他列，那么如前所述，它可能是连接数据中的任何随机值。如果你想要所有人，那么每个人都使用group_concat()。
查看group_concat的手册，因为对于大型数据集，您可能需要增加group_concat_max_len