== Опис

<syntaxhighlight lang="sql">
CREATE OR REPLACE FUNCTION trg_prevent_double_booking()
RETURNS TRIGGER
AS $$
BEGIN
    IF NEW.booking_status IN ('PENDING','CONFIRMED') THEN
        IF EXISTS (
            SELECT 1
            FROM bookings b
            WHERE b.room_id = NEW.room_id
              AND b.booking_status IN ('PENDING','CONFIRMED')
              AND daterange(b.check_in_date, b.check_out_date, '[)')
                  && daterange(NEW.check_in_date, NEW.check_out_date, '[)')
        ) THEN
            RAISE EXCEPTION 'Room % is already booked', NEW.room_id;
        END IF;
    END IF;

    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE TRIGGER prevent_double_booking
BEFORE INSERT ON bookings
FOR EACH ROW
EXECUTE FUNCTION trg_prevent_double_booking();
</syntaxhighlight>