BEGIN
DECLARE overlapping_count INT;

SET overlapping_count = (
SELECT COUNT(*)
FROM reservation
WHERE room_id = NEW.room_id
AND date_out >= NEW.date_in
AND date_in <= NEW.date_out
);

IF overlapping_count > 0 THEN
-- Without that the mesage dont work
SIGNAL SQLSTATE '45000'
SET MESSAGE_TEXT = 'Selected room is not available for the specified dates.';
END IF;
END

(SELECT customer_id
FROM `order`
WHERE quantity>=3;)

Y no funciona

A ver si me dan el logro