Interactive SQL tutorial (SQLzoo.net)
SQL Quick Reference
Database Normalization Basics
Oracle specific, includes questions about SQL Plus commands.
Mostly Oracle specific, need to sign up to see your score.
After taking the test you get a report with your time, your score, your answer for each question, if this is correct or not, and recommended reading for incorrect answers.
20 questions, no time limit, at the end of the Quiz, your total score will be displayed.