|Can I register and play under multiple email addresses?
||Not if you want to compete for rankings and prizes. Playing under multiple email addresses is considered a form of cheating. If you are playing non-competitively (an option you can select on the Player Profile Preferences page), then "no harm, no foul" because you are not competing with others.
You may still win a raffle prize based on participation in the PL/SQL Challenge.
Once you check the box to play non-competitively, you cannot un-check it and start competing again, until the start of a new quarter.