That is a good point, I didn't add in the check to make sure you need to use a sub-query, but it was a hint, and the question text didn't specifically say it HAD to be a sub-query, so use whatever works.

One of the interesting things about SQL in general, is that you can go about the same question multiple ways, and ultimately receive the exact same result. So for a question where we really want you to do the question one way, we have to add in external Python code to check it first, as the output is identical for some operations (e.g. joining tables purely with WHERE or by JOINs).

Adam.

"Mengxi Li" [email protected] wrote:

I think youou can solve the problem both ways,using a subquery with NOT IN,or using a LEFT JOIN to achieve the same result. But the hint encourages the use of a subquery to practice that method. You can have a try with both approaches in your terminal.