text: --- Test constraints
  insert into chat.user (login)
  values ('admin');
  
  
  insert into chat.message ("user", time, value)
  values (currval('chat.user_id_seq'), now(), 'my super user message');
  
  delete from chat.user where login = 'admin';
  
  --- select test
  select *
  from chat.message
  where time > '2017-03-25';
  
  