create table if not exists rel_invitations (
    id uuid not null primary key,
    email text not null,
    base_id uuid not null references bases(id) on delete cascade,
    class_oid oid not null,
    created_by uuid not null references users(id) on delete restrict,
    privilege text not null,
    expires_at timestamptz,
    unique (email, base_id, class_oid, privilege)
);
create index on rel_invitations (base_id, class_oid);
create index on rel_invitations (email);