Question

我有4张桌子。

发布：id，title

标记：id，name

post_tag ：id，post_id，tag_id

user_read_activity ：id，user_id，post_id

User_read_activity包含用户已阅读的帖子。 Post_tag包含链接到标签的帖子。一个帖子可以有多个标签。我需要根据用户关注的某些标记获取用户未读帖子，并删除用户可能不喜欢的某些帖子。

我已经提出了这个代码。但这是错误的。这也给了我用户阅读帖子。但基于标签这些都是正确的。只需要纠正未读部分。请帮帮我。

如果代码错误，也请帮我修改代码。

SELECT DISTINCT post.* FROM post 

INNER JOIN post_tag ON post.id = post_tag.post_id 

INNER JOIN tag 

WHERE tag.id = 21 OR tag.id = 26 OR tag.id = 63 OR tag.id = 86 OR tag.id = 11 

AND post.id != 1088 AND post.id != 338 AND post.id != 1396 

AND post.id NOT IN (SELECT post_id from user_read_activity WHERE user_id = 70)  

ORDER BY post.likes DESC LIMIT 5

Answer 1

您只需要围绕您的条件使用括号来明确优先顺序。您还应该在post_tag和tag之间进行适当的连接：

SELECT DISTINCT post.* FROM post 

INNER JOIN post_tag ON post.id = post_tag.post_id 

INNER JOIN tag ON post_tag.tag_id = tag.id

WHERE (tag.id = 21 OR tag.id = 26 OR tag.id = 63 OR tag.id = 86 OR tag.id = 11)

AND post.id != 1088 AND post.id != 338 AND post.id != 1396 

AND post.id NOT IN (SELECT post_id from user_read_activity WHERE user_id = 70) 

ORDER BY post.likes DESC LIMIT 5

或者@dimwittedanimal建议的IN标准可以使用。

SELECT DISTINCT post.* FROM post 

INNER JOIN post_tag ON post.id = post_tag.post_id 

INNER JOIN tag ON post_tag.tag_id = tag.id

WHERE tag.id IN (21, 26, 63, 86, 11)

AND post.id NOT IN (1088, 338, 1396)

AND post.id NOT IN (SELECT post_id from user_read_activity WHERE user_id = 70) 

ORDER BY post.likes DESC LIMIT 5

Mysql：从多个表中获取数据

1 个答案: