SELECT SUM(STIP) FROM student

SELECT id_stud, AVG(mark) FROM progress HAVING BY id_stud WHERE AVG(mark)>3

SELECT stud_name FROM student WHERE id_stud = ANY (SELECT id_stud FROM progress WHERE mark = 2)

SELECT stud_name FROM student WHERE stip IN (1200, 1300, 1500)

SELECT id_stud FROM progress WHERE mark IS NULL;