text: drop table if exists students;
  drop table if exists invitations;
  
  drop index if exists invitations_by_inviter;
  drop index if exists invitations_by_invitee;
  
  create table students (
      id serial primary key,
      name varchar(64),
      uni varchar(7) unique,
      confirmed boolean default false
  );
  
  create table invitations (
      id serial primary key,
      inviter varchar(7),
      invitee varchar(7),
      message varchar(140),
      confirmed boolean default false,
      email_sent boolean default false,
      unique (inviter, invitee)
  );
  
  create index invitations_by_inviter on invitations (inviter);
  create index invitations_by_invitee on invitations (invitee);
  