audio_guide_hire

CREATE TABLE audio_guide_hire (
  hire_id          INTEGER PRIMARY KEY,
  ticket_id        INTEGER NOT NULL REFERENCES ticket (ticket_id),
  serial_number    TEXT NOT NULL REFERENCES audio_guide_device (serial_number),
  order_id         INTEGER NOT NULL UNIQUE REFERENCES purchase_order (order_id),
  language_code    TEXT NOT NULL REFERENCES language (language_code),
  issued_wing_id   INTEGER NOT NULL REFERENCES wing (wing_id),
  issued_at        TEXT NOT NULL,
  returned_wing_id INTEGER REFERENCES wing (wing_id),
  returned_at      TEXT,
  CHECK ((returned_at IS NULL) = (returned_wing_id IS NULL)),
  CHECK (returned_at IS NULL OR returned_at > issued_at)
) STRICT;