I have a table of tasks:

```
task_id | done_by_user_id
-------------------------
1       | 1
1       | 2
2       | 1
2       | 3
3       | 3
4       | 1

```

The table contains data which task has be solved by which user, whereas each task can be solved by more than one user. I already have a query that groups the tasks and counts how many users have worked on each task: `SELECT task_id, COUNT(*) FROM tasks GROUP BY task_id`

Next, I want to filter all groups by user: When one task was solved by one user, I want that task to be removed from my results. What I first tried was `SELECT task_id, COUNT(*) FROM tasks WHERE done_by_user_id != ? GROUP BY task_id` but that only decreases the count but does not filter the whole group.