events
id

teachers
id

event_teacher
e_id, t_id

SELECT e.id, e.date
FROM events as e
WHERE e.date < '2021-09-08' AND e.id NOT IN (
    SELECT et.event_id
    FROM event_teacher as et
    WHERE et.event_id = e.id
    )
GROUP BY e.id, e.date

TABLE users(id, name);

TABLE managers(id, name);

TABLE problems(id, name);

TABLE tasks(
    id,
    manager_id REFERENCES managers (id),
    problem_id REFERENCES problems (id)
);

TABLE users_tasks(
    user_id INTEGER REFERENCES users (id),
    task_id INTEGER REFERENCES tasks (id),
);

SELECT *
    FROM users
    INNER JOIN users_tasks ON users.id = users_tasks.user_id
    INNER JOIN tasks ON tasks.id = users_tasks.task_id AND tasks.manager_id = 1;

SELECT *
    FROM users
    INNER JOIN users_tasks ON users.id = users_tasks.user_id
    INNER JOIN tasks ON tasks.id = users_tasks.task_id 
WHERE tasks.manager_id = 1;