Okänd kolumn i "ha klausul"

Som skrivet i dokumentationen

Du måste ange return_date och rental_date i select-satsen.

Det finns två alternativ:

SELECT DISTINCT
  customer.first_name,
  rental.return_date,
  rental.rental_date
FROM
  rental,
  customer
WHERE
  rental.customer_id = customer.customer_id
GROUP BY
  rental.rental_id
HAVING
  (
    rental.return_date - rental.rental_date
  ) =(
  ...

eller

SELECT DISTINCT
  customer.first_name,
  (rental.return_date - rental.rental_date) as rental_duration
FROM
  rental,
  customer
WHERE
  rental.customer_id = customer.customer_id
GROUP BY
  rental.rental_id
HAVING
  rental_duration =(
  ...

Båda borde fungera bra.