SELECT * FROM classroom
LEFT JOIN (SELECT lesson.classroom_id, count(lesson.id) as lessons_count
      FROM lesson
        JOIN (SELECT *
              FROM course
              WHERE start_date <= current_timestamp AND finish_date >= current_timestamp) AS alias
          ON lesson.course_id = alias.id
      GROUP BY lesson.classroom_id) as lessons ON lessons.classroom_id = classroom.id
    where classroom.partner_creator_id = 2
;