[英]Selecting from more than two tables using join selects duplicates
I have 3 table on my mysql db (user, follower, post), I wrote an sql, that get all posts from the people a user followed. 我在mysql db(用户,关注者,发布)上有3个表,我写了一个sql,该列表从用户关注的人那里获取所有发布。
sql sql
SELECT post.* FROM post JOIN
follower ON post.owner_user_id = follower.user_id AND
follower.follower_id = "3"
result 结果
id | owner_user_id | content
2 | 1 | why are all my senior developers jerks?
3 | 1 | PHP7 in your face node.js
user table 用户表
id | username | password
1 | user1 | 12345678
2 | user2 | 12345678
3 | user3 | 12345678
follower table 追随者表
user_id | follower_id
3 | 1
3 | 2
1 | 3
post table 发布表
id | owner_user_id | content
1 | 2 | reading a 1k+ page on mysql, do i need to?
2 | 1 | why are all my senior developers jerks?
3 | 1 | PHP7!, in your face node.js
3 | 3 | I posted
so now am trying to select post of people the user is following and the posts of the user 所以现在尝试选择用户关注的人的帖子以及用户的帖子
I tried this sql 我试过这个SQL
sql sql
SELECT post.* FROM post JOIN
follower ON post.owner_user_id = follower.user_id AND
follower.follower_id = "3" JOIN
user ON post.owner_user_id = user.id= "3"
result 结果
null
Please is what am trying to achieve with the sql possible, if(possible) {"what_am_i_doing_wrong"}(); if(可能){“ what_am_i_doing_wrong”}();
edits 编辑
user_id 3 has a post, still running the above sql returns null, was hoping if the user had no post, only post of the people the user is following is returned
select post.* from
(select user_id from follower where follower_id = 3 union select 3) blah
join post on blah.user_id = post.owner_user_id;
Try this: 尝试这个:
SELECT Distinct post.* FROM post JOIN
follower ON post.owner_user_id = follower.user_id JOIN
user ON follower.user_id = user.id WHERE user.id = 3
You shuldn't use conditions in JOIN statement, use WHERE instead. 您不应在JOIN语句中使用条件,而应使用WHERE。
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