MySQL 8.0

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create table users (
  user_id int,
  username varchar(15)
);

insert into users values 
(1,'Marc'),
(2,'Paul'),
(3,'Sofie'),
(4,'Julia');

create table posts (
  post_id int,
  topic_id int,
  poster_id int,
  post_time int
);

insert into posts values 
(4565,6,1,999092051),
(4567,6,4,999094056),
(4333,6,2,999098058),
(7644,6,1,999090055);

Records: 4  Duplicates: 0  Warnings: 0



Records: 4  Duplicates: 0  Warnings: 0


select * from users;
select * from posts;


user_id
username


1
Marc

2
Paul

3
Sofie

4
Julia




post_id
topic_id
poster_id
post_time


4565
6
1
999092051

4567
6
4
999094056

4333
6
2
999098058

7644
6
1
999090055


SELECT 
    p.poster_id, 
    p.post_time, 
    p.post_id,   
    p.post_time,
    u.user_id, 
    u.username                
FROM posts as p 
INNER JOIN users as u ON u.user_id = p.poster_id 
where (p.poster_id, p.post_time )in(select poster_id, max(post_time) from posts group by poster_id ,p.post_time )


poster_id
post_time
post_id
post_time
user_id
username


1
999092051
4565
999092051
1
Marc

2
999098058
4333
999098058
2
Paul

4
999094056
4567
999094056
4
Julia

post_id	topic_id	poster_id	post_time
4565	6	1	999092051
4567	6	4	999094056
4333	6	2	999098058
7644	6	1	999090055