text: create table if not exists conversations (
      cid serial not null
      constraint conversations_pkey
      primary key,
      id integer not null unique,
      name text,
      last_ts integer not null
  );
  
  create table if not exists notifications (
      rid serial not null
      constraint reminders_pkey
      primary key,
      type text not null,
      whom integer not null references conversations on delete no action,
      ts integer not null
  );