Ответы на экзамен

/*1 Запрос*/

select firstname, lastname, middlename
from student
union all
select firstname, lastname, middlename
from teacher
order by lastname

/*2 запрос*/

select s.firstname as Имя_студента, s.lastname as Фамилия_студента,
t.firstname as Имя_учителя, t.lastname as Фамилия_учителя, t.middlename as Отчество_учителя,
count(gb.gradebookid) as Количество_оценок
from student s cross join teacher t
left join gradebook gb on s.studentid = gb.studentid and t.teacherid = gb.teacherid
group by s.studentid, t.teacherid
having count(gb.gradebookid) = 0

/*3 запрос*/

select sum(count)
from ((select count(lastname) as count
from (select firstname, lastname, middlename
from student
union all select firstname, lastname, middlename
from teacher
order by lastname)
group by lastname
having count(lastname) > 1))