task_dr6_7_query.rb

Student.count

Student.where(name: "Иван").count

Student.where(created_at Student.where('created_at >= ?', '2020-09-02 00:00:00').count

Student.where.not(parent_id: nil).count

Student.join(:parents).where( parents: { name: 'Марина'} ).count

Student.where(parent_id: nil).count