According to the hint: "Hint use UNION then an EXCEPT operation." But why? Because the table bookjobs has both cust_id and jobtype, we just need to use EXCEPT like this: SELECT cust_id FROM bookjobs WHERE jobtype IN ('R', 'H') EXCEPT SELECT cust_id FROM bookjobs WHERE jobtype = 'N'; If we use UNION, it should be something like this: SELECT cust_id FROM bookjobs WHERE jobtype = 'R' UNION SELECT cust_id FROM bookjobs WHERE jobtype = 'H' EXCEPT SELECT cust_id FROM bookjobs WHERE jobtype = 'N'; Am I correct or using a wrong database? Thanks.

You are correct in using EXCEPT with IN, as it achieves the same goal. The hint suggests using UNION likely for clarity or to explicitly combine job types 'R' and 'H' before filtering. It is simply an exercise in using UNION, but both approaches should yield the same result in this case.