VL
select * from `schedules` where `user_id` in (select `user_id` from `teachers` where exists (select * from `subjects`такой sql рабочий запрос вышел
inner join `subjects_teachers` on `subjects`.`id` = `subjects_teachers`.`subject_id`
where `teachers`.`id`
= `subjects_teachers`.`teacher_id` and `subject_id` = 2))