sql - 查询连接 2 表和 1 表

Question

抱歉，如果标题与我的问题无关。 我不知道这个的正确标题是什么。

所以我有 5 个表格，以便向用户显示相关内容

1. 内容（id、内容等） Data related content
2. ContentCategory(id, contentId, followCategoryId) Data related content's categories
3. ContentPublisher (id, contentId, followPublisherId) Data related content's publishers
4. FollowCategory(id, categoryId, userId(关注的人), etc..) Data related user's followed categories
5. FollowPublisher（id、publisherId、userId（关注的人）等。） Data related user's followed publishers

如何根据用户的关注类别和关注的发布者显示内容，如果可能，如何区分内容是来自followCategory或followPublisher上的关系

例如：下面是我根据用户 FollowPublisher、cmiiw 显示内容的查询

SELECT content.id, content.description, ...etc 
FROM followPublisher
LEFT JOIN publisher ON followPublisher.publisherId = publisher.id
LEFT JOIN contentPublisher ON publisher.id = contentPublisher.publisherId
RIGHT JOIN content ON contentPublisher.contentId = content.id
    WHERE followPublisher.userId = 8
ORDER BY content.created desc;

以下是我根据用户 followCategory 显示内容的查询

SELECT content.id, content.description, ...etc 
FROM followCategory
LEFT JOIN category ON followCategory.categoryId = category.id
LEFT JOIN contentCategory ON category.id = contentCategory.categoryId
RIGHT JOIN content ON contentCategory.contentId = content.id
    WHERE followCategory.userId = 8
ORDER BY content.created desc;

如何结合这两个查询一次显示基于用户关注的类别和发布者的内容，或者有没有更好的方法而不是结合查询？

Answer 1

我认为您想要以下内容：

select content.* from content
LEFT JOIN contentPublisher ON content.id = contentPublisher.contentId 
LEFT JOIN Publisher ON contentPublisher.publisherId = publisher.id 
LEFT JOIN followPublisher ON publisher.id = followPublisher.publisherId
LEFT JOIN contentCategory ON content.id = contentCategory.contentId 
LEFT JOIN category ON contentCategory.categoryId = category.id 
LEFT JOIN followcategory ON category.id = followcategory.categoryId
where followPublisher.userId = 8 or followCategory.userId = 8

Answer 2

使用联合

有2个条件

• 不要按order by使用任何与表相关的（idk 怎么说），而是使用as重命名它。 在我的情况下， order by content.created应该更改为content.created as contentCreated ，然后我们可以使用它来order by 。

• 添加默认值列以指示数据的来源（在这种情况下，无论是来自followPublisher还是followCategory ）

询问：

SELECT content.id, content.description, content.created as contentCreated ...etc, 'publisher' as type
FROM followPublisher
LEFT JOIN publisher ON followPublisher.publisherId = publisher.id
LEFT JOIN contentPublisher ON publisher.id = contentPublisher.publisherId
RIGHT JOIN content ON contentPublisher.contentId = content.id
    WHERE followPublisher.userId = 8
UNION
SELECT content.id, content.description, content.created as contentCreated ...etc, 'category' as type
FROM followCategory
LEFT JOIN category ON followCategory.categoryId = category.id
LEFT JOIN contentCategory ON category.id = contentCategory.categoryId
RIGHT JOIN content ON contentCategory.contentId = content.id
    WHERE followCategory.userId = 8
ORDER BY contentCreated desc;