zad1.
SELECT student.Nazwisko
FROM student
WHERE student.DataUrodzenia<(SELECT student.DataUrodzenia FROM student WHERE student.IDStudent=student.IDStarosty)
ORDER BY IDGrupy DESC, student.DataUrodzenia

zad2.
DELETE FROM student
WHERE student.IDGrupy=(
        SELECT grupa.IDGrupa FROM grupa WHERE grupa.Nazwa="421"
    )
    AND YEAR(student.DataUrodzenia)<1990

zad3.
UPDATE student SET student.KwotaStypendium=MIN(student.KwotaStypendium)
WHERE student.KwotaStypendium>MIN(student.KwotaStypendium) AND  student.IDGrupy=(SELECT grupa.IDGrupa FROM grupa WHERE grupa.Kampus="B")

zad4.
SELECT grupa.Nazwa ,COUNT(*) FROM student JOIN grupa
ON student.IDGrupy=grupa.IDGrupa
WHERE student.KwotaStypendium>AVG(student.KwotaStypendium)
GROUP BY grupa.Nazwa;

zad5.
SELECT grupa.Nazwa ,COUNT(*) FROM student JOIN grupa
ON student.IDGrupy=grupa.IDGrupa
WHERE student.KwotaStypendium>(SELECT AVG(student.KwotaStypendium) FROM student)
GROUP BY grupa.Nazwa