Intersection with MySQL with queries

I am trying to intersect two querys in MySQL in this fashion:

SELECT user_id FROM post GROUP BY thread_id HAVING COUNT(thread_id) = 1
INTERSECT
SELECT user_id FROM post GROUP BY user_id HAVING COUNT(user_id) = 1;

I've looked for ways to do it in MySQL, but unfortunately using IN and INNER JOIN hasn't worked for me.

The test data I'm working with is:

insert into post (post_number, timestamp, user_id, thread_id) values(0,0,1,1000);
insert into post (post_number, timestamp, user_id, thread_id) values(0,0,2,2000);
insert into post (post_number, timestamp, user_id, thread_id) values(0,0,3,2000);
insert into pos开发者_如何学Ct (post_number, timestamp, user_id, thread_id) values(0,0,4,3000);
insert into post (post_number, timestamp, user_id, thread_id) values(0,0,5,4000);
insert into post (post_number, timestamp, user_id, thread_id) values(0,0,1,4000);

Running an intersection of my two queries should result in

4

Any help is appreciated, thanks.

---

In postgres I'd do it like this

SELECT user_id FROM post where thread_id in (
select thread_id from post group by thread_id having count(distinct user_id) = 1)
INTERSECT
SELECT user_id FROM post GROUP BY user_id HAVING COUNT(user_id) = 1;

However, apparently mysql doesn't support intersect, so an inner join will suffice:

SELECT post.user_id FROM post 
join (SELECT user_id FROM post GROUP BY user_id HAVING COUNT(user_id) = 1) x on x.user_id = post.user_id
where 
post.thread_id in (
select thread_id from post group by thread_id having count(distinct user_id) = 1)

Those both return 4

---

So, you want a list of users who have posted one orphan thread? Maybe a subselect works best.

SELECT user_id
  FROM (
    SELECT user_id
      FROM post
      GROUP BY thread_id
      HAVING COUNT(thread_id) = 1
  ) AS orphan
  GROUP BY user_id
  HAVING COUNT(user_id) = 1

EDIT: Yeah, the above was wrong; I didn't think about it enough. Here's another go, but don't get your hopes up:

SELECT user_id
  FROM (
    SELECT user_id
      FROM post
      GROUP BY thread_id
      HAVING COUNT(thread_id) = 1
  ) AS orphan_post
  INNER JOIN (
    SELECT user_id
      FROM post
      GROUP BY user_id
      HAVING COUNT(user_id) = 1
  ) AS orphan_user
  ON user_id