My feedback after answering the first question:

1. Q0's success messages says "Group by and Having are commonly used aggregate functions". This terminology is incorrect. SUM() is an aggregate function. GROUP BY and HAVING are clauses. 2. Without an ORDER BY clause, there's no guarantee of the order of the result, but the quiz appears to require the output rows to be in the same (in the case of Q0, undefined) order as the expected rows. While this is unlikely to spontaneously change, it's like depending on the order of an unordered hash map. As long as you're teaching people things, it's good to instill the habit of always ordering their results.