select * from course, exams, student where id_student=rk_student and id_course=rk_course
select surname, date_start, title, hours, score from (select * from course, exams, student where id_student=rk_student and id_course=rk_course 

and score=2) as my_subquery
select surname, date_start, title, hours, score from (select * from course, exams, student where id_student=rk_student and id_course=rk_course 

and score>2 and title='Информатика') as my_subquery
select surname, date_start, title, hours, score from (select * from course, exams, student where id_student=rk_student and id_course=rk_course 

and score=5 and YEAR(date_start)=2020) as my_subquery

select * from exams join student on id_student=rk_student join course on id_course=rk_course

select surname, date_start, title, hours, score from (select * from exams join student on id_student=rk_student join course on id_course=rk_course and score=2) as my_subquery