(*
select avg(res) as SREDNII from examen
where e_type=2 and sem_key in
    (select sem_key from sem_his
    where his_key in
        (select his_key from year_his
        where st_id in
            (select st_id from fio
            where surname='Афонина'
              and name='Екатерина')))
 *)
    ADODataSet1.Active:=false;
    ADODataSet1.CommandText:='select avg(res) as SREDNII from examen '+
    'where e_type=2 and sem_key in '+
    '(select sem_key from sem_his '+
    'where his_key in '+
    '(select his_key from year_his '+
    'where st_id in  '+
    '(select st_id from fio '+
    'where surname='+''''+'Афонина'+''''+
    'and name='+''''+'Екатерина'+''''+')))';
    ADODataSet1.Active:=true;