create table states
(
    id            integer
        primary key autoincrement,
    word_id       integer           not null
        references words
            on delete cascade,
    deck_id       integer           not null
        references decks
            on delete cascade,
    score         integer default 1 not null,
    last_opened   integer           not null,
    fsrs_opened   integer           not null,
    fsrs_memory   integer           not null,
    fsrs_open_day integer           not null
);