Unknown column in 'having clause'
As written in the documentation
The SQL standard requires that HAVING must reference only columns in the GROUP BY clause or columns used in aggregate functions. However, MySQL supports an extension to this behavior, and permits HAVING to refer to columns in the SELECT list and columns in outer subqueries as well.
You have to specify return_date and rental_date in the select clause.
There are two options:
SELECT DISTINCT customer.first_name, rental.return_date, rental.rental_dateFROM rental, customerWHERE rental.customer_id = customer.customer_idGROUP BY rental.rental_idHAVING ( rental.return_date - rental.rental_date ) =( ...or
SELECT DISTINCT customer.first_name, (rental.return_date - rental.rental_date) as rental_durationFROM rental, customerWHERE rental.customer_id = customer.customer_idGROUP BY rental.rental_idHAVING rental_duration =( ...Both should work just fine.