CREATE OR REPLACE FUNCTION min_grade_date (task_id number, student_id number)
return varchar
is
    tutor_id number;
    tutor_name varchar;
begin
    select g.tutor_id
    into tutor_id
    from grades g, user_web u, solution s, task t
    where t.id = task_id
    and u.id = student_id
    and s.id = g.solution_id
    and g.grade_date = (select min(grade_date) from grades g, user_web u, solution s, task t
    where t.id = task_id
    and u.id = student_id
    and s.id = g.solution_id);

    select name into tutor_name from user_web where id =  tutor_id;
    return tutor_name;

end;


select distinct s.student_id, t.title, min_grade_date(t.id, s.student_id)
from grades g, user_web u, solution s, task t
where t.id = s.task_id
and s.id = g.solution_id
and u.id = g.tutor_id
order by s.student_id