ALTER TABLE users ADD COLUMN send_results INTEGER NOT NULL DEFAULT 0 CHECK (send_results IN (0, 1));
UPDATE users SET send_results = 1 WHERE is_admin = 1;

CREATE TABLE result_sends (
  draw_id  INTEGER NOT NULL REFERENCES draws(id),
  user_id  INTEGER NOT NULL REFERENCES users(id),
  sent_at  TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
  PRIMARY KEY (draw_id, user_id)
);