使用聯接從兩個以上的表中進行選擇會選擇重復項

Question

我在mysql db（用戶，關注者，發布）上有3個表，我寫了一個sql，該列表從用戶關注的人那里獲取所有發布。

sql

SELECT post.* FROM post JOIN
       follower ON post.owner_user_id = follower.user_id AND
       follower.follower_id = "3"

結果

id | owner_user_id | content
2  | 1             | why are all my senior developers jerks?
3  | 1             | PHP7 in your face node.js

用戶表

id | username | password
 1 | user1    | 12345678
 2 | user2    | 12345678
 3 | user3    | 12345678

追隨者表

user_id | follower_id
3       | 1
3       | 2
1       | 3

發布表

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

所以現在嘗試選擇用戶關注的人的帖子以及用戶的帖子

我試過這個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"

結果

null

if（可能）{“ what_am_i_doing_wrong”}（）;

編輯

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

Answer 1

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;

Answer 2

嘗試這個：

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

您不應在JOIN語句中使用條件，而應使用WHERE。