[Busla]

Видимо, "область науки" - field, "крайняя дата" - DateLimit препод настолько суеверен, что даже в тех.документации избегает слова "последний"?

Код:

select ID.user from user
  inner join (select distinct IDUser, IDConference from application) as app on ID.user=IDUser.app
  inner join conference on IDConference.app=ID.conference
  group by user.id
  having count(IDField.conference)>1;

Код:

update user set Password='please-change-it' where IDentrprise in (select ID from enterprise where Name='Саянский...');

Код:

delete application
  from application
  inner join conference on IDConference.application=ID.conference
  where ApplicationDate.application>DateLimit.conference;

(писал прямо тут, возможны опечатки)