-- Related articles under each web issue article: the nearest embedded articles
-- across the whole archive, computed when the issue is published (and by
-- `features related` for older issues). Stored rather than computed per page
-- view because finding them is a scan of every cached embedding.
CREATE TABLE issue_related (
    issue_date TEXT NOT NULL REFERENCES issues(date) ON DELETE CASCADE,
    article_id INTEGER NOT NULL REFERENCES articles(id) ON DELETE CASCADE,
    position   INTEGER NOT NULL,              -- 0 = closest
    related_id INTEGER NOT NULL REFERENCES articles(id) ON DELETE CASCADE,
    cosine     REAL NOT NULL,
    PRIMARY KEY (issue_date, article_id, position)
);